METHODS  OF  MACHINE  SHOP  WORK 


Frontispiece 


SIR  JOSEPH  WHITWORTH 


METHODS  OF 
MACHINE  SHOP  WORK 


FOR  APPRENTICES  AND  STUDENTS  IN  TECHNICAL 
AND  TRADE  SCHOOLS 


BY 
FREDERICK  A.  HALSEY,  B.  M.  E. 

EDITOR    EMERITUS,    AMERICAN    MACHINIST,    ASSOCIATE    IN    MECHANICAL   ENGINEERING, 
COLUMBIA    UNIVERSITY,    MEMBER,    AMERICAN    SOCIETY    OF    MECHANICAL   ENGI- 
NEERS, AUTHOR,  "SLIDE  VALVE  GEARS,"  "THE  USE  OF  THE  SLIDE 
RULE,"     "WORM     AND     SPIRAL     GEARING,"     "THE  METRIC 
FALLACY,"     "HANDBOOK    FOR    MACHINE    DESIGNERS 

AND    DRAFTSMEN,"    ETC. 


FIRST  EDITION 
FIFTH  IMPRESSION 


McGRAW-HILL  BOOK  COMPANY,  INC. 
NEW  YORK:  370  SEVENTH  AVENUE 

LONDON:  6  &  8  BOUVERIE  ST.,  E.  C.  4 
1914 


H3 


COPYRIGHT,  1914,  BY  THE 
MCGRAW-HILL  BOOK  COMPANY,  INC. 


PRINTED    IN   THE   UNITED    STATES    OF    AMERICA 


THK- MAPLE- PRESS- YORK. PA 


PREFACE 

While  the  printed  page  cannot  take  the  place  of  personal 
experience,  there  is,  nevertheless,  a  great  fund  of  information 
regarding  tools,  methods  and  processes  that  can  be  acquired 
from  the  printed  page  more  effectively  than  from  any  other 
source.  Effective  as  the  " picking  up"  process  is  as  regards 
the  things  picked  up,  it  passes  by  many  which  are  equally 
important  and  it  has,  at  best,  no  logical  order  or  sequence,  the 
information  so  gathered  being  unassorted,  fragmentary  and 
incomplete.  Few  machine  shops  make  use  of  more  than  a 
small  fraction  of  the  methods  which  are  herein  explained  and 
which  the  properly  informed  should  know  but  the  learning  of 
which  commonly  requires  half  a  lifetime.  While  many  of  the 
methods  shown  are  the  commonplaces  of  the  experienced 
mechanic,  they  have  not,  heretofore,  been  gathered  together 
in  print,  and  still  less  have  their  underlying  principles  or  their 
mutual  relationships  been  explained  for  the  use  of  beginners. 
It  is  to  the  explanation  of  these  things  that  the  printed  page  is 
best  adapted  and  to  which  these  pages  are  chiefly  devoted. 

The  volume  comprises  the  substance  of  the  lectures  which 
the  author  has  presented  to  the  students  in  mechanical  engineer- 
ing at  Columbia  University  for  the  past  three  years.  It  has 
been  prepared  in  the  belief,  which  is  shared  by  friends  who  have 
been  consulted,  that  it  would  prove  useful  elsewhere,  in  trade 
as  well  as  engineering  schools  and  to  apprentices. 

The  volume  presupposes  no  more  than  a  reasonable  famili- 
arity with  the  more  common  machine  tools,  their  general  con- 
struction, uses  and  fields  of  application;  in  other  words  such  a 
degree  of  mechanical  intelligence  as  should  be  acquired  by  an 
apprentice  in  serving  one  or,  at  most,  two  years  in  any  modern 
machine  shop. 

The  chapters  relating  to  actual  machine  tools  might  have  been 
expanded  indefinitely.  In  the  embarrassment  due  to  the 
voluminous  material  available,  the  author,  in  addition  to  show- 
ing basic  principles,  has  chosen  to  present  the  less  obvious 
features,  passing  by  many  which,  while  equally  important, 
are  reasonably  certain  to  be  gathered  in  the  course  of  everyday 
experience.  To  those  manufacturers  who  may  feel  aggrieved 
because  their  own  products  have  not  been  included,  although 
in  many  cases  as  meritorious  as  those  shown,  the  author  would 

vii 

692743 


viii  PREFACE 

explain  that  his  object  is  to  show  methods,  not  machines,  the 
appearance  of  the  machines  being  incidental  to  the  showing  of 
the  methods.  When  choice  has  been  necessary,  preference  has 
usually  been  given  to  those  machines  which  first  introduced  a 
given  method. 

The  reader  as  well  as  the  author  is  under  large  obligations  to 
the  manufacturers  who  have  so  liberally  supplied  the  photo- 
graphs from  which  the  half-tone  illustrations  have  been  made 
and  the  more  so  because,  in  numerous  cases,  the  illustrations 
do  not  show  things  made  for  sale.  Such  photographs  have 
been  supplied  in  the  true  educational  spirit — a  spirit  that  has 
gone  so  far  as  to  lead  to  the  making  of  special  exposures  when 
suitable  negatives  were  not  available.  When  old  negatives 
had  been  destroyed  and  the  making  of  new  ones  was  imprac- 
ticable, existing  engravings  have  been  reproduced,  chiefly 
from  the  pages  of  the  American  Machinist  where,  in  fact,  the 
counterparts  of  most  of  those  made  from  new  photographs 
first  appeared. 

The  machine  shop  is  the  center  from  which  all  modern 
industries  radiate.  From  the  brickyard  to  the  flying  machine, 
from  the  sawmill  to  wireless  telegraphy,  from  the  stone  quarry 
to  the  moving-picture  camera,  there  is  no  modern  industry 
more  than  twice  removed  from  the  machine  shop.  Of  the 
works  of  man  it  is  to  the  author  the  most  interesting  place  on 
earth  and  in  this  spirit  this  volume  is  offered,  not  only  as  a 
source  of  instruction  to  the  succeeding  generation,  but  as  a 
tribute  to  those  great  mechanics,  living  and  dead,  of  this  and 
other  lands,  whose  active  brains  and  deft  fingers  have  created 
the  marvels  of  which  the  attempt  is  here  made  to  portray 
some  of  the  inner  spirit. 


CONTENTS 


PAGE 

PREFACE    .  vii 


INTRODUCTION i 

CHAPTER  I 

THE  Two  SYSTEMS  OF  MACHINE  PRODUCTION 3 

The  making  and  manufacturing  systems  defined  and  contrasted — 
The  machine  tools  characteristic  of  each,  their  place  of  origin, 
development  and  distinguishing  characteristics — Early  develop- 
ments of  accurate  measurements  in  Great  Britain  and  the  United 
States — Early  history  of  the  manufacturing  system — Basic  features 
of  the  two  systems — Effect  of  the  measuring  system  on  shop  organi- 
zation, workmanship  and  business  policy. 

CHAPTER  II 

PRECISION  WORK  AND  WORKMANSHIP 23 

Interchangeability  and  high  accuracy  not  synonymous — Tendency 
of  all  machine  work  toward  degradation  of  workmanship — 
Precision  workmanship  checks  this  tendency — The  three  kinds  of 
accuracy — Originating  flat  surfaces — Uses  of  such  standards — 
Originatng  squares  and  other  angles  by  the  scraping  process — 
Other  methods  of  originating  squares  and  angles — Uses  of  such 
standards — The  principle  of  the  division  of  functions — Originating 
index  plates — Originating  index  worm  wheels. 

CHAPTER  III 

MEASURES  OF  LENGTH 65 

The  metric  fallacy — The  origin  of  measures  of  length — Relative 
accuracy  of  line  and  end  measures — Relation  of  accuracy  of 
measurement  to  character  of  surfaces — Source  of  error  in  shop  use 
of  line  measures — Methods  of  avoiding  this  source  of  error — Early 
history  of  measuring  machines — The  line  measure  as  a  standard — 
Characteristic  features  of  modern  measuring  machinos — The 
micrometer  caliper — Precision  lathes  for  cutting  precision  screws. 

CHAPTER  IV 

THE  MEASUREMENT  OF  ERRORS 97 

Instruments  for  measuring  errors  embodying  the  multiplying  lever 
— Uses  of  these  instruments — The  dial  gage  and  its  uses — The 
measurement  of  errors  with  extemporized  apparatus. 

ix 


x  CONTENTS 

CHAPTER  V 

PAGE 
GAGES m 

Relation  of  stiffness  and  sensitiveness  of  gages — In  large  gages  stiff- 
ness must  be  sacrificed  to  lightness — Expedients  used  under  these 
conditions — Defects  of  snap  gages — Explanation  of  the  popularity 
of  common  calipers — Limit  gages — Improved  construction  of  snap 
gages — Causes  which  restrict  the  use  of  gages — The  Johansson 
combination  gages,  their  principles  and  properties — Uses  of  these 
gages — Screw  thread  gages — Independent  measurements  of  the  va- 
rious elements  of  screw  threads — Measuring  the  errors  of  pitch  of 
long  screws. 

CHAPTER  VI 

FITS  AND  LIMITS 135 

The  limit  system  of  manufacture — Definition  of  terms — The  shaft 
and  the  hole  bases  for  fits — Differences  between  American  and 
British  practice — Influence  of  the  grinding  machine — Examples  of 
tolerances  in  various  kinds  of  work — Taper  fits. 

CHAPTER  VII 

DRIVING  SYSTEMS  FOR  MACHINE  TOOLS 143 

The  three  leading  systems  of  driving  and  their  proper  fields  of  use 
— Defects  of  the  old  type  of  cone  pulley  and  methods  of  overcoming 
them — Individual  vs.  group  motor  driving. 

CHAPTER  VIII 

TURNING  AND  BORING 151 

The  primitive  engine  lathe — Lathes  for  work  of  large  diameter  and 
great  length — The  boring  mill,  plain  and  turret — The  turret  lathe — 
Special  tools  and  their  cost — The  collet  chuck — The  pilot  bar — 
Reamers  and  reaming — The  automatic  turret  lathe — The  magazine 
feed — The  multiple  spindle  automatic  turret  lathe — The  multau- 
matic  machine — The  Fay  and  Lo-swing  lathes — The  three  types  of 
boring  bars  and  their  uses — Taper  and  spherical  boring  bars — 
Vertical  boring  machines  for  large  engine  cylinders. 

CHAPTER  IX 

FLOOR-PLATE  WORK 191 

The  floor-plate  system  of  machine  tools — Such  tools  have  no  defined 
limit  of  capacity — Uses  of  the  various  tools — The  floor-plate  boring 
mill. 

CHAPTER  X 

DRILLING 199 

Types  of  drilling  machines — Jigs  and  their  uses — Gang,  multiple- 
spindle  and  station  drilling  machines — The  laying-out  machine  for 
the  accurate  spacing  of  holes — The  base  line  system  of  drawings — 
Other  methods  of  spacing  holes — The  master  plate. 


CONTENTS  xi 

CHAPTER  XI 

PAGE 

MILLING 224 

Early  development  of  the  milling  machine — Advantages  of  the 
constant-speed  drive  as  applied  to  milling  machines — Vertical- 
spindle  milling  machines — Types  of  milling  cutters — Uses  of  the 
milling  machine — The  rotary  planter — The  profiling  machine — 
The  cam-cutting  machine — The  screw-thread  milling  machine 
— The  milling  cutter  grinder. 

CHAPTER  XII 

GEAR  CUTTING 250 

Multiplicity  of  forms  of  gear-cutting  machines — The  advantages  of 
the  diametrical  pitch  system — The  three  basic  systems  of  gear 
cutting — Machines  enbodying  these  systems — Bevel  gear-cutting 
machines — The  octoid  system  of  bevel  gear  teeth — Gear-molding 
machines. 

CHAPTER  XIII 

GRINDING 270 

Early  development  of  the  grinding  machine — Rough  turning  and 
finish   grinding — Uses   of   the   grinding   machine — The    planetary 
grinding  machine — The  surface  grinding  machine. 
INDEX  .        ,   281 


INTRODUCTION 

The  object  of  this  volume  is  to  show  how  the  problems  of  the 
shop  are  attacked  and  solved — not  to  show  how  machine  tools  are 
operated.  This  plan  necessitates  giving  considerable  attention 
to  precision  work  which,  in  turn,  emphasizes  the  intellectual 
character  of  the  work — a  feature  which  cannot  fail  to  impress 
the  reader  and  give  him  increased  respect  for  those  who  are 
responsible  for  the  methods  and  solutions  herein  set  forth. 
These  methods  relate  largely  to  the  work  of  the  tool  maker, 
which  has  now  reached  a  stage  of  development  which  almost 
entitles  it  to  be  called  a  profession.  In  this,  tool  making  is 
unique  among  occupations  commonly  called  manual.  Its 
development  to  the  point  where  manual  skill  alone  is  helpless 
is  a  matter  of  the  past  fifty  or  sixty  years  and  the  development 
is  one  the  like  of  which  was  never  seen  before. 

An  attempt  has  been  made  to  give  credit  for  the  leading 
inventions  which  mark  the  development  of  the  machine  shop. 
The  author  is  well  aware  that  in  doing  this  he  is  treading  on 
dangerous  ground,  as  few  things  are  more  difficult  than  the 
apportionment  of  credit  for  these  things.  For  this  there  are 
several  reasons.  Frequently  the  first  appearance  of  an  in- 
vention is  in  such  shadowy  form  as  to  make  the  identification 
of  its  origin  difficult  and  even  impossible.  Frequently  great 
inventions  are  of  a  composite  character — different  elements 
being  supplied  by  different  men — and  in  many  cases  of  this 
kind  the  various  elements  are  useless  until  combined  by  some 
one  who  does  nothing  else.  Frequently  the  original  suggestion 
came  at  a  time  when  the  collateral  arts  were  not  sufficiently 
developed  to  make  the  use  of  the  invention  possible  and  it  had 
to  be  reinvented  at  a  later  date.  In  such  cases  it  is  a  subject  of 
dispute  which  inventor  is  entitled  to  the  greater  credit. 
Some  consider  the  chief  credit  due  to  him  who  made  the  effective 
invention,  as  it  is  certainly  to  him  that  the  world  is  indebted 
for  its  use.  In  many  cases  this  is  just  and  proper  because  of 
the  fight,  at  first  with  inertia  and  later  with  infringers,  with 
often,  in  the  end,  defeat  and  despair  and  the  passing  on  of  the 

1 


INTRODUCTION 


Jbeasfits:  to  letters",  which  too  often  accompany  the  introduction 
of  an  invention  and  which  should  not  be  forgotten  when  ap- 
portioning the  credit.  On  the  other  hand,  in  many  cases  it  is 
unjust  because  a  later  inventor  is  frequently  merely  more 
fortunate  in  time  and  circumstance.  Even  more  unjustly, 
inventions  which  are  perfectly  applicable  at  their  first 
appearance,  frequently  lie  dormant  for  many  years  through 
nothing  but  indifference  and  inertia.  Add  to  these  considera- 
tions the  scanty  records  of  industrial  developments  that  exist, 
and  the  difficulties  of  apportioning  credit  for  these  things 
become  apparent,  as  do  the  reasons  for  the  disputes  between 
friends  of  rival  inventors. 

Prof.  J.  W.  Roe  has  summed  up  his  view  of  the  matter  in 
these  words: 

"  It  is  not  easy  to  assign  the  credit  of  an  invention  to  individuals.  Mere 
priority  of  suggestion  or  even  of  experiment  seems  hardly  sufficient. 
Nearly  every  great  improvement  has  been  invented  independently  by  a 
number  of  men,  sometimes  almost  simultaneously,  often  in  widely  sepa- 
rated times  and  places.  Of  these,  the  one  who  made  it  a  success  is  usually 
found  to  have  united  a  superior  mechanical  skill  to  the  element  of  invention. 
He  first  has  embodied  the  invention  in  such  proportions  and  mechanical 
design  as  to  make  it  commercially  available,  and  from  him  its  permanent 
influence  spreads,  and  the  chief  credit  is  due  the  one  who  impressed  it  on 
the  world.  Some  examples  may  illustrate  this  point. 

"Leonardo  da  Vinci  in  the  fifteenth  century  anticipated  many  of  the 
modern  tools.  His  sketches  are  fascinating  and  show  a  wonderful  and 
fertile  ingenuity,  but  while  we  wonder,  we  smile  at  their  proportions. 
Unless  a  later  generation  of  mechanics  had  arisen  to  reinvent  and  redesign 
these  tools,  mechanical  engineering  would  still  be  as  unknown  as  when  he 
died. 

"The  slide-rest  is  clearly  shown  in  the  French  Encyclopedia  of  1772, 
and  even  in  an  edition  of  1717.  Bramah,  Bentham  and  Brunei,  in  Eng- 
land, and  Sylvanus  Brown,  in  America,  are  all  said  to  have  invented  it. 
David  Wilkinson,  of  Pawtucket,  R.  I.,  was  granted  a  patent  for  it  in  1798. 
But  the  invention  has  been,  and  will  always  be,  credited  to  Henry  Mauds- 
ley,  of  London.  It  is  right  that  it  should  be,  for  he  first  designed  and  built 
it  properly,  developed  its  possibilities,  and  made  it  generally  useful.  The 
modern  slide-rest  is  a  lineal  descendant  from  his. 

"Blanchard  was  by  no  means  the  first  to  turn  irregular  forms  on  a  lathe. 
The  old  French  rose  engine  lathe  embodied  the  idea,  but  Blanchard  accom- 
plished it  in  a  way  which  was  more  mechanical  and  which  is  in  general 
use  to  this  day." 


METHODS  OF  MACHINE 
SHOP  WORK 

CHAPTER  I 
THE  TWO  SYSTEMS  OF  MACHINE  PRODUCTION 

The  making  and  manufacturing  systems  defined  and  contrasted— 
The  machine  tools  characteristic  of  each,  their  place  of  origin,  develop- 
ment and  distinguishing  characteristics — Early  developments  of  accurate 
measurements  in  Great  Britain  and  the  United  States — Early  history  of 
the  manufacturing  system — Basic  features  of  the  two  systems — Effect  of 
the  measuring  system  on  shop  organization,  workmanship  and  business 
policy. 

THE  MAKING  AND  MANUFACTURING  SYSTEMS 

There  exist  two  sharply  contrasted  systems  of  machine  pro- 
duction called  respectively  the  making  and  the  manufacturing 
system.  Under  the  first  term  are  included  the  methods  em- 
ployed when  machines  are  produced  one  at  a  time  or,  at  most, 
in  such  limited  numbers  that  the  methods  used  are  not 
essentially  affected  by  the  number.  The  second  term  refers  to 
the  methods  followed  in  wholesale  production  of  interchange- 
able parts. 

Of  these  terms  manufacturing  is  suitable  and  appropriate 
but  as  much  cannot  be  said  of  making.  Properly  considered, 
the  latter  term  is  applicable  to  all  methods,  but  it  has  come  to 
be  used,  and  will  here  be  regularly  used,  in  this  restricted  sense. 
For  this  there  is  excellent  warrant,  as  these  terms  were  used  in 
these  senses  by  Charles  Babbage  in  his  Economy  of  Machinery 
and  Manufactures  published  in  1832,  in  which  these  words  were 
defined  in  a  manner  which  might  be  used  to-day. 

While  the  system  used  is  commonly  determined  by  the 
number  of  things  made,  nevertheless  the  distinction  between 
the  systems  lies  in  the  methods  employed  and  not  in  the 
quantities  produced.  Because  A  makes  a  few  things  of  a  kind 

3 


4  METHODS  OF  MACHINE  SHOP  WORK 

and  B  makes  many,  it  does  not  follow  of  necessity  that  A  works 
under  the  making  and  B  under  the  manufacturing  system. 
If  we  are  unwise  we  may  make  things  in  large  numbers  and  so 
also  we  may  manufacture  things  in  comparatively  limited 
numbers.  The  two  systems  are  frequently  used  conjointly  in 
the  production  of  a  single  product.  For  instance,  in  the  produc- 
tion of  Corliss  engines,  the  larger  parts,  of  which  each  machine 
contains  but  one  and  which  differ  with  each  size  of  engine  pro- 
duced, are  naturally  made,  whereas  the  smaller  parts  of  the 
valve  gear,  of  which  each  machine  contains  several,  one  size  of 
which  may  be  used  on  several  sizes  of  engines  and  which,  by 
reason  of  their  smaller  dimensions,  are  better  adapted  to 
manufacturing  processes,  may  be  manufactured. 

MACHINE  TOOLS  CHARACTERISTIC  OF  THE  SYSTEMS 

For  the  making  system  and  the  machine  tools  by  which  it  is 
carried  on,  we  are  indebted  to  England,  while,  for  the  manu- 
facturing system  and  the  machine  tools  which  are  characteristic 
of  it,  the  United  States  has  the  chief  credit.  Other  countries 
have  supplied  plenty  of  things  to  make — Germany  gave  us  the 
gas  engine,  France  the  automobile  and  Sweden  the  steam 
turbine — but  the  methods  of  machine  production  are  almost 
exclusively  the  work  of  the  English-speaking  peoples. 

The  machine  tools  employed  in  the  making  process  are 
commonly  called  the  standard  tools  and  they  comprise  the  lathe, 
the  planer,  the  shaping  machine,  the  slotting  machine,  the 
boring  mill,  drilling  and  gear-cutting  machines,  all  of  which 
originated  in  England  and  were  brought  to  a  high  state  of 
perfection  there  by  the  close  of  the  first  half  of  the  last  century. 
With  the  exception  of  drilling  and  gear-cutting  machines,  the 
characteristic  feature  of  these  machines  is  that  the  workman 
determines  the  dimensions  of  the  work  by  direct  measurement 
and  by  the  adjustment  of  the  cutting  tools  for  each  piece  as 
made. 

Without  attempting  to  trace  the  earlier  development, 
though  without  forgetting  the  work  of  Maudsley,  who  intro- 


THE  TWO  SYSTEMS  OF  MACHINE  PRODUCTION  5 

duced  the  mechanical  control  of  cutting  tools,  it  may  be  said 
that  "the  beginning  of  practice  that  has  endured"  is  found  in 
the  work  of  John  G.  Bodmer  whose  work  was  done  about 
1840.  Judged  by  present  standards,  the  machine  tools  ante- 
dating Bodmer's  work  were  primitive,  while  Bodmer's  were  not. 
It  may  be  fairly  said  that  Bodmer  started  machine-tool  design 
on  lines  which  it  has  ever  since  followed.  Bodmer's  tool- 
building  enterprise  was,  however,  a  business  failure,  and  the 
effective  introduction  of  modern  designs  is  found  in  the  work 
of  Sir  Joseph  Whitworth  who  left  a  wider  and  deeper  mark  on 
machine-shop  methods  and  practice  than  any  one  else.  He 
built  a  great  works  which  still  exists.1  For  years  his  was  a 
name  to  conjure  with.  No  one  else  has,  or  can  in  future, 
occupy  a  similar  position.  Bodmer  and  Whitworth  were  two 
of  a  great  galaxy  of  mechanical  giants  who  laid  the  foundations 
of  the  manufacturing  industries  of  Great  Britain  and  of  the 
world,  some  of  the  others  being  Watt  of  the  steam  engine, 
Murdock  who  was  Watt's  superintendent  and  who  invented 
gas  lighting,  Trivithick  who  introduced  high-pressured  steam, 
Babbage  of  the  calculating  machine,  Stephenson  of  the  loco- 
motive, Arkwright  and  Hargreaves  of  textile  machinery,  and 
Naysmith  of  the  steam  hammer. 

The  leading  characteristics  of  Whitworth's  work  were  high- 
class  workmanship,  massive  construction,  hollow  frame  mem- 
bers, appropriate  design,  proper  distribution  of  metal,  smooth 
surfaces,  rounded  corners,  straight  lines  or  long  sweeping  curves, 
and  appropriate  paint. 

An  adequate  idea  of  the  advanced  character  of  Whitworth's 
work  may  be  obtained  from  Fig.  i,  which  illustrates  a  Whit- 
worth lathe  (now  preserved  at  the  University  of  Manchester) 
from  designs  made  in  1849. 

While  all  of  the  machine  tools  which  characterize  the  mak- 
ing process  originated  in  England,  in  some  cases  their  develop- 
ment in  the  United  States  outran  that  in  England.  This  is 
especially  true  of  the  boring  mill  which,  although  originally 
designed  by  Bodmer,  became  an  established  and  common  tool 
in  the  United  States  several  decades  in  advance  of  its  general 

1  Consolidated  with  the  works  of  Sir  W.  G.  Armstrong. 


6 


METHODS  OF  MACHINE  SHOP  WORK 


acceptance  in  England.  Similarly,  while  gear-cutting  machines 
originated  in  England,  their  development  into  automatic  ma- 
chines and  the  reduction  of  gear  cutting  to  a  manufacturing 
basis  took  place  in  the  United  States.  This  latter  involved 
the  general  acceptance  of  the  diametral  pitch  system  which, 
although  originated  by  Bodmer  and  used  by  some  in  England, 


FIG.  i.— Whitworth  lathe  of  1849. 

was  introduced  into  general  practice  by  the  Brown  and  Sharpe 
Manufacturing  Company  through  their  production  of  diametral 
pitch  cutters  as  an  article  of  manufacture. 

This  adoption  of  the  diametral  pitch  system  was  both  a  case 
and  an  illustration  of  the  manufacturing  spirit  and  of  manu- 
facturing methods.  If  a  single  pair  of  gears,  including  the 
cutters,  is  to  be  made,  the  circular  pitch  system  is  as  appropri- 
ate and  perhaps  more  appropriate  than  the  diametral  pitch  system 


THE  TWO  SYSTEMS  OF  MACHINE  PRODUCTION  7 

and,  in  fact,  is  still  commonly  used  for  heavy  or  mill  gearing. 
For  small  cut  gears,  especially  when  made  for  interchangeable 
sets,  and  with  the  cutters  produced  as  an  article  of  manufacture 
by  specialists,  as  they  must  be  if  they  are  to  be  of  high  grade, 
the  diametral  pitch  system  has  every  advantage,  by  reason  of 
its  reducing  the  problem  of  gear  cutting  to  a  manufacturing 
basis,  and  for  such  gears  it  is  and  has  long  been  in  universal  use 
in  the  United  States. 

With  the  standard  tools  provided,  the  Englishman  found 
himself  equipped  for  doing  almost  anything  required  and 
activity  in  the  development  of  machine  tools  practically  ceased. 
New  machine  tool  building  shops  were  started,  largely  by 
ambitious  young  men  who  had  learned  their  trade  with  Whit- 
worth,  but  they  copied  Whitworth's  designs — the  best  thing 
that  could  be  said  about  any  machine  tool  being  that  it  was  as 
good  as  Whitworth's.  New  machine  tool  building  shops  were 
started  in  the  United  States  in  much  the  same  way,  but  here 
the  product  offered  was  usually  something  different  from 
existing  designs.  Often,  in  fact,  the  shop  was  started  because 
of  a  burning  desire  to  launch  a  new  idea.  In  Great  Britain 
this  would  have  been  unsafe,  because  of  the  overshadowing 
authority  and  influence  of  the  name  of  Whitworth,  and  in  this 
way  the  same  man  acted  at  one  period  as  a  most  powerful 
influence  for  progress  and  at  a  later  period  as  an  almost  equally 
powerful  influence  for  stagnation.  This  period  of  stagnation 
came  to  an  end  during  the  first  years  of  the  present  century, 
when  active  development  was  resumed.  In  Great  Britain  the 
period  of  stagnation  is  commonly  charged  to  the  antagonism 
of  the  trade  unions  to  more  productive  machines  and,  no  doubt, 
that  antagonism  was  a  contributory  cause. 

The  keynote  of  English  machine-tool  design  is  and  always  has 
been  quality  and  serviceability — a  fact  to  which  it  is  impossible 
not  to  render  ungrudging  acknowledgment,  and,  in  some 
fields  of  work,  notably  steam-boiler  construction,  British  work 
still  leads  in  this  characteristic. 

The  machine  tools  and  equipment  characteristic  of  the 
manufacturing  system  are  the  milling  machine,  including  the 
profiling  machine  and  the  automatic  gear  cutter,  the  turret 


8  METHODS  OF  MACHINE  SHOP  WORK 

lathe,  including  the  automatic  turret  lathe,  the  grinding 
machine,  the  multiple  spindle  drilling  machine  and  all  manner 
of  special  machines,  gages  and  fixtures  or  jigs.  Of  these  the 
plain  milling  machine,  although  originally  developed  in  con- 
nection with  the  manufacturing  system,  has  now  found  large  use 
in  the  making  system,  this  extension  of  its  field  having  taken 
place  first  in  England. 

In  contrast  with  the  standard  tools  the  characteristic  feature 
of  these  machines,  the  grinding  machine  excepted,  is  that  the 
cutting  tools  are  adjusted  to  a  certain  size  which  they  reproduce 
in  the  work,  piece  after  piece,  until  they  become  dull,  when 
they  are  sharpened  and  readjusted. 

While  the  original  appearance  of  the  principle  of  some  of 
these  machines  was  in  primitive  and  obscure  forms  which  cannot 
always  be  identified,  it  is  nevertheless  a  fact  that  their  chief 
development,  their  acceptance  as  means  of  production  and,  in 
most  cases,  their  original  invention  took  place  in  the  United 
States.  This  was  due  to  the  combined  influence  of  the  high 
cost  of  labor  and  a  large  homogeneous  home  market.  The 
former  stimulated  the  search  for  methods  which  reduced  the 
labor  cost,  while  the  latter  justified  the  increased  investment 
of  capital  required  by  these  methods. 

Without  meaning  to  imply  that  quality  has  been  lost  sight  of 
for  machine  work  in  the  United  States  is,  and  for  many  decades 
has  been,  equal  to  that  done  elsewhere,  it  is  nevertheless  true, 
that  the  impelling  motive  of  American  machine-tool  design  has 
been  quantity — mass  production. l 

THE  BEGINNING  OF  ACCURATE  MEASUREMENTS 

It  should,  however,  be  pointed  out  that  one  essential  element 
of  the  manufacturing  system,  without  which,  indeed,  it  would 
be  impossible,  namely,  standard  gages,  originated  in  England 
and  at  the  hands  of  Mr.  Whitworth,  who,  moreover,  recognized 
that  "the  soul  of  manufacture  is  duplication,"  and  Charles 

1  To  this  the  grinding  machine  is  a  conspicuous  exception,  as  it  is  an  exception 
to  nearly  all  general  statements  that  can  be  made.  Its  original  object  was  the 
improvement  of  quality  and  it  was  only  after  it  was  put  into  use  that  it  was 
discovered  that  along  with  improved  quality  went  increased  quantity. 


THE  TWO  SYSTEMS  OF  MACHINE  PRODUCTION  9 

Babbage  clearly  pointed  out  the  advantages  of  mass  production 
in  1832. 

As  with  so  many  other  things,  Whitworth's  gage  work  was 
foreshadowed  by  that  of  Bodmer  who  invented  plug  and  ring 
gages  and  had  them  in  use  in  his  own  shop,  but  it  was  Whitworth 
who  first  produced  them  with  a  grade  of  workmanship  entitled 
to  the  name  of  precision  and  who  made  them  available  to 
others  by  offering  them  for  sale.  This  was  done  about  1850, 
from  which  date  down  to  about  1880  the  Whitworth  works  were 
the  world's  headquarters  for  instruments  of  this  character 
which,  during  all  that  period,  could  be  obtained  nowhere  else. 

Meanwhile  a  corresponding  development  was  taking  place 
in  the  United  States  in  the  improvement  of  line  measures  or 
graduated  scales  which  Whitworth  neglected  because  of  his 
erroneous  belief  in  the  fundamentally  superior  accuracy  of 
end  measures.  In  1850  D.  R.  Brown  produced  a  graduating 
machine  and  about  two  years  later  Samuel  Darling  produced 
another,  both  of  which  were  of  such  accuracy  that  they  are  still 
in  use  at  the  Brown  and  Sharpe  works.  As  a  contribution  to 
the  development  of  accurate  measurements,  the  Brown  and 
Sharpe  scales  have  a  place  alongside  the  Whitworth  gages.  A 
recent  examination  of  one  of  these  scales  of  two  feet  length, 
made  in  1868,  showed  no  error  greater  than  two  ten- thou- 
sandths of  an  inch.  In  185 1  Mr.  Brown  brought  out  the  vernier 
caliper,  substantially  in  the  form  now  used  and  shown  in  Fig.  53, 
which  was  the  first  American  contribution  to  measurements 
of  precision  grade. 

This  was,  however,  more  than  a  precision  instrument.  Giving 
as  it  did  all  sizes  within  its  capacity,  it  was  not  only  accurate 
but  at  the  same  time  so  low  in  cost  as  to  be  available  for  gen- 
eral use. 

For  reasons  which  are  explained  later,  plug  and  ring  gages  are 
not  well  adapted  to  shop  use  and,  for  such  use,  they  have  been 
displaced  by  others,  chiefly  the  solid  caliper  or  snap  gage  which 
was  invented  by  John  Richards  who  had  a  set  of  such  gages 
made  by  the  Brown  and  Sharpe  Manufacturing  Company 
in  1865  and  who  patented  the  design  in  1867.  In  1877  Mr. 
Richards  undertook  the  regular  manufacture  of  these  gages, 


10  METHODS  OF  MACHINE  SHOP  WORK 

relying  upon  an  imported  Whitworth  measuring  machine  to 
originate  the  sizes,  but  this  was  found  so  inaccurate  that  it 
could  not  be  used  and,  about  two  years  later,  he  completed  a 
measuring  machine  of  his  own  design.  The  John  M.  Rogers 
Works  is  the  lineal  descendant  of  the  gage-making  business 
established  by  Mr.  Richards,  which  was  the  pioneer  in  the 
production  of  solid  caliper  gages  for  sale. 

Prior  to  the  construction  of  Mr.  Richard's  measuring  machine 
one  shown  in  Fig.  57  was  completed  in  1874  by  Dr.  John  E. 
Sweet  at  the  Cornell  University  shop  and  exhibited  at  the 
Centennial  Exhibition  of  1876,  which  was  the  first  American 
machine  of  this  character.  It  was  intended  to  form  the  basis 
of  the  manufacture  of  solid  caliper  gages,  but  the  attempt 
to  make  such  gages  in  any  considerable  number  failed,  because 
of  the  imperfect  action  of  abrasive  grinding  wheels  as  then  made. 

The  development  of  the  subject  at  the  Brown  and  Sharpe 
works  had  in  the  meantime  made  a  measuring  machine  neces- 
sary there,  and  the  first  of  the  present  Brown  and  Sharpe  type 
was  completed  in  1878.  In  1882  the  Rogers-Bond  comparator 
for  comparing  line  and  end  measures  was  completed  at  the 
Pratt  and  Whitney  works,  measuring  machines  being  offered 
for  sale  by  this  company  in  1892.  Both  these  companies  pro- 
duced gages  which  far  surpassed  those  of  Whitworth  in  accuracy, 
comparisons  by  independent  parties  of  gages  made  by  the  two 
companies  showing  perfect  agreement.  The  two  companies 
had  independently  copied  the  standard  yard  at  Washington 
and  divided  their  copies,  the  agreement  of  their  product  being 
the  most  satisfactory  proof  possible  of  the  work  of  both. 

THE  BEGINNINGS  OF  THE  MANUFACTURING  SYSTEM 

It  is  not  to  be  supposed  that  the  manufacturing  system  is 
the  outgrowth  of  the  tools  which  have  been  named  in  the  pre- 
ceding pages.  On  the  contrary,  the  tools  are  the  outgrowth 
of  the  system,  which  originated  and  was  practiced  on  a  large 
scale  at  a  time  when  the  tool  equipment  available  was  of  the 
simplest  kind.  The  system  was  first  developed  for  the  manu- 
facture of  small  arms  which  were  the  first  mechanical  devices 


THE  TWO  SYSTEMS  OF  MACHINE  PRODUCTION  11 

required  in  large  numbers,  and  its  beginning  appears  to  have 
been  in  France. 

Thomas  Jefferson,  writing  from  Paris  to  John  Jay  under  date 
of  May  30,  1785,  says: 

"An  improvement  is  made  here  in  the  construction  of  muskets  which 
it  may  be  interesting  to  Congress  to  know,  should  they,  at  any  time, 
propose  to  procure  any. 

"It  consists  in  making  every  part  so  exactly  alike  that  what  belongs 
to  any  one  may  be  used  for  every  other  musket  in  the  magazine." 

In  a  letter  to  the  Governor  of  Virginia,  dated  Jan.  24,  1786, 
Mr.  Jefferson  testifies  that  he  has  examined  the  gun  locks  and 
says:  "I  found  them  to  fit  interchangeably  in  the  most  perfect 
manner." 

The  most  famous  early  example  of  true  manufacturing 
methods  is  the  production  of  blocks  for  ship's  rigging  by  a  series 
of  forty-four  special  machines  designed  by  Sir  Samuel  Bentham 
and  Sir  Marc  Isambard  Brunei  and  made  by  Henry  Maudsley. 
The  machines  were  put  at  work  in  1808  and  continued  to 
supply  the  British  navy  with  blocks  so  long  as  wood  continued 
in  use  for  the  purpose. 

These  examples  seem,  however,  to  have  been  of  a  sporadic 
character  and  to  have  exerted  but  little  influence  on  contem- 
porary or  subsequent  industry.  The  effective  beginning,  which 
was  followed  by  general  adoption  in  not  only  its  own  but  in 
many  other  industries,  is  found  in  the  production  of  small 
arms  for  the  United  States  army. 

This  beginning  was  due  to  Eli  Whitney — he  of  the  cotton 
gin — who  in  1798  contracted  to  make  10,000  muskets  for  the 
United  States  Government.  That  these  guns  were  inter- 
changeable we  again  have  the  testimony  of  Jefferson  who, 
writing  to  Monroe  in  1801,  said  of  Whitney: 

"He  has  invented  molds  and  machines  for  making  all  the  pieces  of 
his  locks  so  exactly  equal,  that  take  100  locks  to  pieces  and  mingle 
their  parts  and  the  100  locks  may  be  put  together  by  taking  the  pieces 
which  come  to  hand." 

Equally  definite  and  more  competent  testimony  is  found  in  a 
report  rendered  in  1800  by  Capt.  Decius  Wadsworth,  inspector 


12 


METHODS  OF  MACHINE  SHOP  WORK 


of  muskets,  to  the  Secretary  of  the  Treasury.1  The  system 
then  adopted  for  the  manufacture  of  American  small  arms  be- 
came and  has  remained  the  characteristic  feature  of  their  pro- 
duction and  the  U.  S.  Armory  at  Springfield,  Mass.,  became, 


FIG.  2. — The  genesis  of  the  manufacturing  system. 


1  Almost  contemporaneous  with  Whitney's  contract  was  one  executed  with 
Col.  Simeon  North  for  500  horse  pistols,  and,  although  this  contract  was  ob- 
tained fourteen  months  after  Whitney's,  deliveries  under  it  began  earlier.  In 
a  biography  of  Colonel  North  by  his  descendants,  priority  in  the  use  of  the 
interchangeable  system  is  claimed  for  him.  That  he  used  the  system  in  the 
execution  of  this  contract  is  not  improbable,  although  the  proof  is  less 
categorical  than  in  the  case  of  Whitney. 

The  first  contract  in  which  interchangeability  was  stipulated  was  awarded  to 
North  in  1813  for  20,000  pistols,  the  stipulation  reading:  "The  component  parts 
of  pistols  are  to  correspond  so  exactly  that  any  limb  or  part  of  one  pistol  may  be 
fitted  to  any  other  pistol  of  the  twenty  thousand."  The  appearance  of  such  a 
requirement  in  a  contract  indicates  that  the  system  was  already  established,  as 
no  prudent  contractor  would  guarantee  such  a  feature  in  advance  of  actual 
experience  with  the  system. 

Just  when  the  requirement  of  interchangeability  became  the  established  custom 
is  not  known,  but  in  a  contract  with  North  for  pistols,  dated  Nov.  16,  1826,  the 
phrase  "uniform  locks  and  the  usual  uniform  component  parts"  appears. 

Both  Whitney  and  North  had,  for  their  time,  large  and  well  equipped  armories 
— the  former  at  Whitneyville,  now  part  of  New  Haven,  and  the  latter  at  Berlin 
and  later  at  Middletown,  Conn.  Both  continued  to  make  small  arms  for  the 
government  until  the  end  of  their  lives — the  former  in  1825  and  the  latter  in  1852. 
North  made  both  muskets  and  pistols — the  number  of  the  latter  aggregating  not 
less  than  50,000. 


THE  TWO  SYSTEMS  OF  MACHINE  PRODUCTION  13 

later,  the  nursery  from  which  the  system  was  transplanted  and 
became  the  recognized  American  system  of  production. 

Beyond  the  fact  that  Whitney  invented  and  used  the  milling 
machine,  almost  nothing  is  known  of  his  methods.1  The 
earliest  record  of  interchangeable  methods  of  which  the  author 
has  knowledge  is  shown  in  Fig.  2,  which  is  from  relics  found  at 
the  Springfield  Armory  and  which  shows  the  methods  used 
in  making  the  lock  plate  of  the  Springfield  musket  of  1855. 
When  this  picture  was  originally  taken  other  relics  showing 
similar  methods  and  dating  as  far  back  as  1840  were  found,  but 
in  these  older  cases  the  exhibits  were  incomplete  and  did  not 
show  the  entire  process  as  does  this. 

THE  ESSENTIAL  DISTINCTION  BETWEEN  THE  SYSTEMS 

At  the  upper  right-hand  corner  will  be  seen  the  forging  for 
the  lock  plate  as  it  came  from  the  smith  shop.  Below  is  the 
same  plate  after  having  had  its  flat  surfaces  milled  and  some 
holes  drilled  through  it.  In  the  upper  left-hand  corner  the 
same  piece  is  again  seen  between  two  templets  or  filing  jigs, 
the  inner  plates  of  which  are  of  hardened  steel.  The  jig  with 
the  forging  in  position  as  shown  was  placed  in  a  vice  and  the 
workman,  with  a  common  file,  reduced  the  outline  of  the  lock- 
plate  to  that  of  the  filing  jig.  At  the  bottom  of  the  illustration 
the  same  piece  is  seen  after  additional  work  had  been  done  upon 
it,  and  in  process  of  being  gaged  by  insertion  in  a  receiver  gage 
of  hardened  steel  by  which  the  uniformity  of  the  various 
pieces  was  tested  and  determined. 

The  thing  to  be  especially  noted  in  this  illustration  is  the  gage 
and  the  fact  that  the  gun  part  was  made  to  fit  this  gage  instead 
of  being  made  to  fit  a  mating  part  of  the  gun.  There  is  every 

Colonel  North's  armory  was  of  sufficient  importance  to  have  been  included  in 
the  itinerary  of  General  Lafayette  who  visited  it  on  the  occasion  of  his  re-visit 
to  the  United  States  in  1824,  and  at  this  armory  were  made  the  pair  of  gold- 
mounted  pistols  presented  to  Commodore  Isaac  Hull  by  the  State  of  Connecticut 
in  1820.  These  pistols  are  now  preserved  in  the  Navy  Department  at  Washing- 
ton and  are  beautiful  specimens  of  the  armorer's  art. 

The  Winchester  Repeating  Arms  Company  is,  by  purchase,  the  successor  of 
Whitney's  business.  That  of  North  long  since  disappeared. 

1  One  of  Whitney's  milling  machines — believed  to  be  his  first — is  preserved  at 
Yale  University. 


14  METHODS  OF  MACHINE  SHOP  WORK 

testimony  that  these  guns  were  interchangeable,  and  it  is  obvious 
from  the  methods  followed  that  there  is  no  reason  why  they 
should  not  have  been.  Interchangeability  is  the  determining 
feature  of  the  manufacturing  system  and  we  find  in  this  case  true 
manufacture,  although  the  cutting  tool  used — a  common  file- 
was  among  the  simplest  of  all. 

The  feature  that  makes  this  a  case  of  true  manufacture  is  the 
fact  that  the  part  was  made  to  fit  a  gage  and  this  points  out  the 
fundamental  distinction  between  the  making  and  the  manu- 
facturing systems,  which  lies  not  in  the  methods  of  production 
but  in  the  system  of  measurement.  In  the  making  system 
we  use  line  measures  or  graduated  scales,  while  in  the  manufac- 
turing system  we  use  end  measures  or  gages  and  it  is  here  that 
the  distinction  between  the  two  systems  lies.  All  other  differ- 
ences that  can  be  pointed  out  are  differences  of  degree,  while 
this  difference  is  one  of  kind. 

While  these  methods  now  seem  extremely  simple  and  even 
primitive,  it  is  not  to  be  understood  that  the  workmanship  was 
poor.  On  the  contrary,  many  old  specimens  of  armorers'  work 
are  beautiful  examples  of  workmanship. l  Simple  as  the  methods 
now  seem,  there  is  ample  proof  of  their  advanced  character, 
measured  by  the  standards  of  their  time,  as  the  following 
extracts  from  the  autobiography  of  James  Naysmith  will  show: 

"In  1853  I  was  appointed  a  member  of  the  Small-arms  Committee  for 
the  purpose  of  remodelling  and,  in  fact,  reestablishing  the  Small-arms 
Factory  at  Enfield  .  .  .  The  United  States  government,  though  pos- 
sessing only  a  very  small  standing  army,  had  established  at  Springfield 
a  small-arms  factory  .  .  .  The  government  resolved  to  introduce  the 
American  system  .  .  . 

.  .  .  "The  committee  resolved  to  make  a  personal  visit  to  the  United 
States  factory  at  Springfield.  My  own  business  engagements  at  home 
prevented  my  accompanying  the  members  .  .  .  The  United  States 
government  acted  most  liberally  in  allowing  the  committee  to  obtain  every 
information  on  the  subject  .  .  . 

"The  members  of  the  mission  returned  home  enthusiastically  delighted 
with  the  results  of  their  inquiry.  The  committee  immediately  proceeded 
with  the  entire  remodelling  of  the  Small-arms  Factory  at  Enfield.  The 

1  The  fit  of  mating  pieces  is  just  as  apparent  under  one  system  of  production 
as  another,  and  the  old  mechanics  possessed  a  skill  of  hand  which,  so  far  as  making 
the  parts  fit  one  another  was  concerned,  answered  all  requirements. 


THE  TWO  SYSTEMS  OF  MACHINE  PRODUCTION  15 

workshops  were  equipped  with  a  complete  series  of  special  machine  tools, 
chiefly  obtained  from  the  Springfield  factory." 

EARLY  PROGRESS  OF  THE  MANUFACTURING  SYSTEM 

At  the  beginning  of  the  Civil  War  the  manufacturing  sys- 
tem was  well  developed  as  measured  by  its  results — inter- 
changeability.  Moreover,  mechanical,  as  distinguished  from 
hand,  methods  had  been  applied  to  a  number  of  operations. 
The  drop  hammer,  the  turret  lathe,  the  milling  machine,  the 
drilling  jig,  the  Blanchard  lathe  for  gun  stocks  and  other 
special  machines  were  in  use,  most  of  those  named  being  well 
established.  When  the  war  began,  the  enormous  demand 
for  small  arms  for  the  Union  forces  led  to  further  great 
developments.  These  were  brought  about  largely  by  the 
cooperation  of  the  authorities  at  the  Springfield  Armory 
and  the  firm  of  Pratt  and  Whitney  which  recently  had  been 
established  at  Hartford.  The  demand  for  small  arms  could 
not,  however,  be  supp'ied  by  the  Armory  and  the  Govern- 
ment advertised  for  bids  from  private  manufacturers.  Other 
business  being  prostrated  by  the  war,  manufacturers  having 
shops  adapted — or  thought  to  be  adapted — to  the  work, 
bid  for  contracts  and,  the  prices  being,  under  the  circum- 
stances, large  and  safe,  they  obtained  them.  They  then  went 
to  Springfield  to  learn  how  the  work  was  done  and  from 
there  they  went  home  and  adopted  the  same  general  methods. 
The  war  over,  the  demand  for  guns  ceased  but,  meanwhile,  a 
great  educational  work  had  been  done.  The  sewing  machine 
was  just  ready  to  become  a  household  appliance  and  to  its 
production  the  same  general  methods  were  applicable  and  were 
applied.  The  same  was  true  of  agricultural  machinery  and 
other  things  were  added  from  time  to  time.  The  application 
of  the  system  to  clock  and  watch  making  was  made  prior  to 
the  war,  the  former  (according  to  Prof.  J.  W.  Roe)  by 
Chauncey  Jerome  about  1830  and  the  latter  by  A.  L.  Dennison 
at  Waltham  in  1848. 

It  was  in  this  way  that  the  knowledge  of  manufacturing  meth- 
ods was  extended  and  they  became  characteristic  American 
methods.  The  progress  made  at  Springfield  was  soon  recog- 


16  METHODS  OF  MACHINE  SHOP  WORK 

nized  abroad.  In  the  early  yo's  the  German  armories  at 
Spandau,  Erfurt  and  Danzig  were  largely  reequipped  with 
Pratt  and  Whitney  tools  and  later,  though  on  a  less  extensive 
scale,  came  the  refitting  of  the  armories  of  France,  Russia, 
Sweden  and  Denmark.1 

LINE  AND  END  MEASURES  AND  THEIR  USE 

The  names,  line  measure  and  end  measure,  are  common  and  of 
them  the  former  is  a  good,  because  a  descriptive,  name.  The 
latter  is  not  so  good  because  less  descriptive.  It  correctly 
describes  some  but  not  all  of  the  instruments  to  which  it  is 
applied.  Fig.  3  shows  a  group  of  end  measures  of  which  those 


FIG.  3. — Various  forms  of  ena  measures. 

in  the  upper  left-hand  corner  are  called  rod  gages,  the  dimension 
which  they  give  being  the  distance  between  their  ends.  At  the 
right  is  the  plug  and  ring  construction,  substantially  as  made  by 
Whitworth.  In  the  lower  group  of  views  are  shown  solid 
caliper  gages — or  snap  gages  in  shop  vernacular — the  one  at  the 
left  being  for  external  and  the  one  in  the  middle  for  internal 
measurements.  The  external  and  internal  gages  are  frequently 
combined  in  the  same  instrument  as  shown  in  the  lower  right- 
hand  corner. 

Of  these  the  rod  gages  are  typical  end  measures,  although  the 
solid  caliper  or  snap  gage  is  the  most  usual  form.     The  plug  and 

author  repeats  these  facts  as  he  heard  them  from  the  lips  of  F.  A.  Pratt. 


THE  TWO  SYSTEMS  OF  MACHINE  PRODUCTION  17 

ring  gages  are  not  adapted  for  direct  use  in  gaging  parts  and  were 
not  intended  for  such  use  by  Whitworth.  His  plan  was  to  sub- 
stitute a  set  of  these  gages  for  the  customary  graduated  scales 
and  then  have  the  workman  adjust  his  calipers  to  them — the  size 
of  the  work  being  simply  a  repetition  of  the  size  of  the  gage. 

It  will  be  observed  that,  in  the  use  of  line  measures,  the  sense 
of  sight  is  employed,  whereas,  in  the  use  of  end  measures,  we 
use  the  sense  of  touch  and  hence  these  two  kinds  of  instruments 
are  sometimes  called  sight  and  touch  measures  which  names  are 
better  than  the  customary  line  and  end  measures. 

An  obvious  difference  between  these  two  types  of  measuring 
instruments  is  that,  within  the  limits  of  its  graduations  and 
length,  the  line  measure  gives  all  sizes  while  the  end  measure 
gives  one  size  only,  for  which  reason  an  equipment  of  end 
measures  is  far  more  expensive  than  one  of  line  measures. 
Another  difference  is  that  while  the  line  measure  does  not  lose 
its  accuracy  because  of  wear  the  end  measure  suffers  deteriora- 
tion from  that  cause. 

When  making  two  mating  parts  by  the  use  of  a  line  measure, 
say  a  shaft  and  its  bearings,  the  procedure  is  to  take  the  size 
from  the  graduated  scale  with  a  pair  of  calipers  and  proceed  to 
make  one  piece.  The  size  of  the  mating  piece  is  obtained  by 
transferring  from  that  of  the  first  by  outside  and  inside  calipers. 
If  the  second  piece  is  made  immediately,  the  same  initial  ad- 
justment of  the  calipers  may  be  used,  but,  if  made  later,  the 
calipers  are  first  adjusted  to  the  first  piece  and  then  transferred, 
when  the  second  piece  is  made  to  fit  the  first.  There  is,  how- 
ever, always  a  difference  between  the  sizes  of  the  two  pieces  in 
accordance  with  their  use.  If,  as  in  the  case  supposed,  one 
piece  is  to  turn  within  the  other,  it  must  be  smaller  by  an 
amount  sufficient  for  lubrication.  If,  on  the  other  hand,  one 
piece  is  to  be  forced  within  the  other,  as  in  the  case  of  a  steam- 
engine  shaft  and  its  crank,  the  first  piece  must  be  larger  than 
the  bore  of  the  second.  Under  the  procedure  described,  these 
allowances  for  the  fit  are  left  to  the  judgment  and  skill  of  the 
workman.1 

1  This  statement  refers  to  the  older  practice,  which,  however,  is  still  in  large 
use.    In  the  better  shops  using  the  making  system  the  allowances  for  the  fits  are 
now  obtained  by  the  micrometer. 
2 


18  METHODS  OF  MACHINE  SHOP  WORK 

It  will  be  seen  that  the  basic  feature  of  this — the  making — 
system  is  that  one  part  is  made  to  a  line  measure  while  the  sec- 
ond part  is  made  to  fit  the  first. 

On  the  other  hand,  when  manufacturing  parts,  the  procedure 
is  to  make  one  hundred,  one  thousand,  or  ten  thousand  of  both 
mating  pieces  to  end  measure  gages  and  then  assemble  them 
expecting  that  they  will  fit — the  allowance  for  the  fit  appearing 
in  the  gages — and  this  is  the  basic  feature  of  the  manufacturing 
system. 

THE  INFLUENCE  OF  THE  MEASURING  SYSTEM  ON  FACTORY 
ORGANIZATION  AND  WORKMANSHIP 

The  effect  of  this  difference  of  procedure  is  a  profound  one 
and  it  affects  the  entire  organization  of  the  factory. 

Under  the  making  system  the  responsibility  for  the  workman- 
ship is  divided.  The  lathe  hand  determines  the  lathe  fits,  the 
planer  hand  the  planer  fits  and  the  vice  hand  the  hand-made  fits. 
In  doing  this  they  have  the  large  advantage  of  being  able  to  com- 
pare the  parts  by  inserting  one  within  the  other  and  thus  bring 
direct  judgment  to  bear  on  the  suitableness  of  the  fits.  They 
do  not  need  to  think  in  thousandths  of  an  inch  nor  even  to  have 
any  definite  idea  of  their  value.  As  a  matter  of  fact,  before 
the  days  of  the  micrometer  caliper,  although  making  fine  fits, 
they  had  no  such  definite  knowledge  and  always  looked  upon 
such  a  dimension  as  the  thousandth  of  an  inch  with  derision,  un- 
til actually  shown  by  that  instrument  that  they  had  been  habit- 
ually making  fits  that  required  working  well  within  this  limit. 

Under  the  manufacturing  system, -in  place  of  this  division  of 
responsibility,  we  have  concentration  of  responsibility  on  the 
gage  maker  for,  when  making  the  gages,  he  must  determine  the 
fits.  He  must  do  this  for  all  grades  of  work  and  for  parts  with 
the  direct  production  of  which  he  has  nothing  to  do  and  which, 
in  fact,  he  seldom  sees.  Because  of  this  he  must  possess  some- 
thing more  than  that  intangible  thing  which  we  call  skill.  To 
skill  he  must  add  that  very  tangible  thing  which  we  call  knowl- 
edge and  that  most  tangible  of  all  tangible  knowledge  which  can 
be  expressed  in  figures. 

It  will  be  seen  that  the  whole  gage  system  is  simply  a  me- 
chanical application  of  a  geometrical  axiom — things  which  are 


THE  TWO  SYSTEMS  OF  MACHINE  PRODUCTION  19 

equal  to  the  same  thing  are  equal  to  each  other — and,  looking 
back  at  the  old  piece  of  armory  work  shown  in  Fig.  2,  we 
realize  again,  and  more  forcibly  than  before,  that,  in  spite  of' 
their  laborious  character,  the  piece  shown  was  produced  by 
true  manufacturing  methods. 

To  one  who  has  been  brought  up  under  the  older  method  of 
trying  parts  together  and  who  knows  how  very,  very  little  is 
required  to  spoil  a  fit,  the  adoption  of  the  gage  method  requires 
courage.  The  mating  parts  are  made  by  different  men  to  fit 
gages  made  by  other  men.  They  are  made  at  different  times 
and,  most  likely,  in  widely  separated  parts  of  the  factory.  From 
the  place  of  production  they  are  sent  to  a  store  room  to  be  with- 
drawn promiscuously  as  needed  and  sent  to  the  assembling  de- 
partment, perhaps  months  after  they  were  made,  in  the  ex- 
pectation that  they  will  fit.  All  this  requires  faith— not  merely 
faith  in  a  geometrical  axiom,  but  faith  in  tools,  in  men,  in  meth- 
ods, and  in  the  team  work  of  the  entire  organization. 

The  story  of  the  manufacturing  system  is  not,  however,  all 
written  on  one  side  of  the  shield,  for  the  system  has  its  limita- 
tions and  its  disadvantages.  To  begin  with,  the  investment  is 
enormous.  The  cost  of  gages  as  compared  with  line  measures 
has  already  been  pointed  out  and,  while  the  gages  are  but  a  small 
part  of  the  factory  equipment,  their  cost  as  compared  with  that 
of  line  measures  may  be  taken  as  illustrative  of  the  comparative 
cost  of  equipment  for  production  by  the  two  methods.  The 
machine  tools  which  have  now  become  identified  with  the  manu- 
facturing system  are  far  more  expensive  than  the  much  simpler 
tools  which  suffice  for  the  making  system  and,  added  to  their 
first  cost,  comes  a  large  outlay  for  special  fixtures  and  jigs  of  all 
kinds.  This  increased  cost  of  equipment  leads  to  a  corre- 
sponding increase  in  interest  and  depreciation  charges  and  the 
more  so  because  much  of  the  special  equipment  is  short- 
lived. In  the  conduct  of  the  system  a  tool-making  depart- 
ment must  be  installed  and  manned  by  high-priced  men,  and 
this  department  produces  nothing  that  sells.  There  must  be  a 
higher  class  and  an  increased  number  of  superintendents  and 
foremen  all  down  the  line  to  the  inspectors,  all  of  which  leads 
to  a  heavy  increase  of  the  overhead  charge  or  burden. 


20  METHODS  OF  MACHINE  SHOP  WORK 

The  development  of  the  manufacturing  system  has  reached 
the  point  where,  in  many  instances,  the  direct  labor  cost  has 
almost  reached  the  vanishing  point,  but  against  this  the  over- 
head charge  has  increased.  Formerly  the  chief  item  of  cost  in 
producing  machinery  was  the  wages  paid  for  direct  labor,  but 
to-day  the  direct  labor  and  the  overhead  have  changed  places, 
the  latter  being  much  the  larger  of  the  two  and  the  question  is 
frequently  and  legitimately  asked  if,  after  all,  the  new  condition 
is  as  healthy  as  the  old. 

It  is  easy  to  ask :  What  difference  does  it  make?  If  the  total 
cost  has  gone  down,  as  it  has,  why  should  one  care  if  the  dis- 
tribution of  the  cost  between  labor  and  overhead  has  been 
changed?  The  reply  is  that  the  difficulties  of  the  new  system 
manifest  themselves  in  seasons  of  dull,  business.  Under  the 
older  system  in  which  the  chief  outgo  is  in  wages  to  direct  labor, 
the  dismissal  of  some  of  the  workmen  in  dull  seasons  reduces 
the  outgo  to  a  degree  not  differing  largely  from  the  reduced 
volume  of  business.  Under  the  newer  system,  however,  with 
the  overhead  far  exceeding  the  direct  wages,  the  dismissal  of 
some  of  the  workmen  has  no  such  effect.  The  overhead,  in 
turn,  is  substantially  fixed  and  can  be  reduced  but  little  and, 
adjusted  as  it  must  be  to  the  conditions  of  active  trade  and  the 
chief  item  of  the  outgo  under  those  conditions,  it  becomes 
ruinous  when  distributed  over  the  smaller  output  of  dull 
seasons. 

The  entire  manufacturing  system  is  predicated  upon  a 
large  output  and  this  compels  the  manufacturer  to  make  goods 
of  a  grade  for  which  there  is  a  large  demand.  There  is  thus  a 
relationship  between  the  manufacturing  system  and  the 
workmanship  of  the  product,  but  this  relationship  is  so  many 
sided  that  a  comprehensive  summary  of  it  is  almost  impossible. 
There  are  cases  in  which  the  system  distinctly  improves  the 
output,  a  conspicuous  example  being  the  making  of  balls,  which 
are  now  made  by  the  million,  with  a  degree  of  accuracy  and 
uniformity  surpassing  any  other  mechanical  product  except 
gages,  and  one  which  would  be  an  absolute  impossibility  under 
the  making  system.  Another  example  is  found  in  machine 
screws  which  are  turned  out  in  enormous  quantities  and  with  a 


THE  TWO  SYSTEMS  OF  MACHINE  PRODUCTION  21 

degree  of  precision  that  would  be  entirely  impossible  under  the 
making  system. 

The  maintenance  of  a  proper  standard  under  the  making 
system  would,  in  many  cases,  involve  prohibitive  cost,  and 
under  these  circumstances,  which  are  illustrated  by  the  manu- 
facture of  typewriters  and  adding  machines,  the  manufacturing 
system  not  only  improves  the  workmanship,  but  does  more  by 
making  the  production  of  such  machines  of  suitable  workman- 
ship a  commercial  possibility.  There  are  other  cases  in  which 
there  is  no  need  of  a  high  quality  of  workmanship,  an  example 
being  found  in  agricultural  machinery  in  which  a  high  quality 
of  workmanship  would  be  absurd.  In  still  other  cases  it  is 
undoubtedly  true  that  the  general  tendency  of  the  system  is 
toward  the  production  of  products  of  medium  and  cheap 
grades,  examples  of  this  tendency  being  seen  in  the  enormous 
present  day  production  of  cheap  clocks  and  watches.  Even 
in  such  cases,  however,  the  system  improves  the  quality  of  the 
product  which  is  purchasable  at  a  given  price,  and  even  makes 
possible  the  production  of  products  which,  otherwise,  could  not 
be  produced  at  all. 

Another  effect  of  the  system  is  the  outgrowth  of  the  enormous 
investment  in  plant  which  it  demands,  a  large  part  of  which  is 
for  equipment  designed  for  and  adapted  to  the  production  of 
the  particular  thing  produced  and  which  must  be  scrapped  when 
changes  are  made.  The  effect  of  this  is  to  postpone  improve- 
ments— the  desire  to  make  improvements  being  held  in  check 
by  the  knowledge  that  they  call  for  large  additional  capital 
investment. 

THE  INFLUENCE  OF  WORKMANSHIP  ON  COST 

There  is  no  doubt  that  the  standard  of  workmanship  of  manu- 
factured goods  is  rapidly  improving  or,  more  properly,  ex- 
tending. This  latter  word  is  used  because  progress  in  these 
matters  is  not  a  matter  of  yesterday  or  the  day  before.  In 
some  things  Whitworth  set  the  highest  standard  that  prevails 
to-day  three-quarters  of  a  century  ago.  Watt  made  a  microm- 
eter caliper  over  a  century  ago  and  Whitworth's  crowning 
achievement — a  measuring  machine  which  did  unquestionably 


22  METHODS  OF  MACHINE  SHOP  WORK 

indicate  differences  of  dimensions  of  a  millionth  of  an  inch — was 
publicly  exhibited  in  1851.  These  citations  will  show  that  the 
conception  of  accuracy  and,  in  some  cases,  its  realization  are  by 
no  means  recent  and  that  present  day  achievements  are  the 
outgrowth  of  the  gradual  development  of  the  constructive  arts 
rather  than  of  the  conception  of  and  desire  for  higher  standards. 

The  extension  of  accurate  workmanship  is  largely  due  to  the 
growing  knowledge  of  the  fact  that  up  to  a  certain  (or  uncertain) 
point  the  product  is  made  more  cheaply  as  the  workmanship  is 
improved — a  fact  that  grows  out  of  the  increased  economy  of 
assembling  when  the  parts  are  well  made.  If  the  parts  are  not 
alike,  fitting  must  be  resorted  to  during  the  process  of  assembling 
and,  in  complex  machines  like  typewriters  or  adding  machines, 
the  expense  of  this  would  be  ruinous.  On  the  other  hand,  if  the 
parts  are  alike,  the  assembling  becomes  little  more  than  placing 
and  securing  them  in  position. 

This  point  up  to  which  improved  workmanship  cheapens  the 
product  cannot  be  defined,  but  beyond  it  further  improvement 
of  quality  increases  the  cost  at  a  rapid  rate  and  nothing  is  more 
important  than  a  realization  of  this  fact.  Because  of  it 
mechanical  enthusiasm  must  constantly  be  held  in  subjection  to 
sound  judgment.  At  every  point  the  question  must  be  asked, 
is  not  this  good  enough?  This  phrase  "good  enough"  is  sub- 
ject to  much  unmerited  criticism.  As  a  matter  of  fact,  no 
commercial  product  is  produced  of  any  better  grade  than  that 
which  the  producer  considers  good  enough.  This  subject  is 
treated  at  greater  length  at  the  conclusion  of  the  chapter  on 
Fits  and  Limits. 


CHAPTER  II 
PRECISION  WORK  AND  WORKMANSHIP 

Interchangeability  and  high  accuracy  not  synonymous — Tendency  of 
all  machine  work  toward  degradation  of  workmanship — Precision  work- 
manship checks  this  tendency — The  three  kinds  of  accuracy — Originating 
flat  surfaces — Uses  of  such  standards — Originating  squares  and  other 
angles  by  the  scraping  process— Other  methods  of  originating  squares  and 
angles — Uses  of  such  standards — The  principle  of  the  division  of  func- 
itons — Originating  index  plates — Originating  index  worm  wheels. 

THE  INHERENT  TENDENCY  TOWARD  DEGRADATION  OF 
WORKMANSHIP 

It  is,  no  doubt,  by  this  time  clear  to  the  reader  that  inter- 
changeability  and  high  accuracy  are  not  synonymous,  although 
there  is  a  very  common — almost  vulgar — impression  that  they 
are  synonymous.  Interchangeability  by  itself  means  little  more 
than  that  the  holes  shall  be  larger  than  the  plugs — the  amount 
by  which  they  are  larger  being  a  matter  of  workmanship  and 
not  of  Interchangeability.  A  concrete  example  of  interchange- 
ability  without  accuracy  is  found  in  stove  lids  which  never  fail 
to  interchange,  but  which  no  one  ever  called  accurate.  The 
remarkable  thing  about  an  interchangeable  machine  is  not  that 
it  is  interchangeable  but  that,  being  interchangeable,  it  is  also 
well  made.  It  is  an  easy  thing  to  make  stove  lids  interchange- 
able, but  interchangeable  watches  are  another  story  and 
between  stove  lids  and  watches  the  essential  difference  is  one 
of  workmanship. 

Any  discussion  of  manufacturing  methods  is  thus  inextricably 
bound  up  with  the  subject  of  accuracy,  by  which  is  meant  not 
high  accuracy  but  the  degree  of  accuracy  suitable  to  the  product 
and  the  means  by  which  it  is  obtained. 

In  all  machine  work  there  is  an  inherent  tendency  toward 
degradation  of  workmanship.  The  manufactured  product  is 

23 


24 


METHODS  OF  MACHINE  SHOP  WORK 


never  as  good  as  the  gages  to  which  it  must  conform  and  it  is 
very  seldom  as  good  as  the  machine  tools  on  which  it  is  made. 
This  tendency  arises  from  several  causes  and  is  of  such  funda- 
mental importance  as  to  require  the  giving  of  concrete  examples. 
Assume  the  dividing  head  of  a  universal  milling  machine  to 
be  set  up  for  the  purpose  of  cutting  some  gears.  The  dividing 
head  of  the  Cincinnati  Milling  Machine  Company  is  shown  in 
Fig.  4,  and  like  all  others,  it  contains  three  parts  whose  accuracy 
determines  the  accuracy  of  the  spacing  of  the  gear  teeth.  These 
are  the  worm  wheel  a,  on  the  work  spindle  b,  the  worm  c  by 
which  this  worm  wheel  is  driven  and  the  index  plate  d  by  which 


FIG.  4. — Section  of  milling  machine  dividing  head. 

the  divisions  are  determined.  If  the  dividing  head  is  by  a  first 
class  maker,  all  of  these  parts  are  of  a  high  degree  of  precision 
but  the  maker  would  be  the  last  man  to  claim  them  to  be 
perfect.  The  spacing  of  the  teeth  of  the  worm  wheel  is  not 
absolutely  uniform,  the  thread  of  the  worm  is  not  a  perfect 
helix  and  the  spacing  of  the  index  plate  holes  is  likewise  not 
absolutely  uniform.  All  of  these  parts  contain  errors  of  a  mag- 
nitude such  that  they  can  be  found  and  measured. 

As  the  gear  blank  is  turned  from  tooth  to  tooth,  these  three 
parts  assume  various  relative  positions  and  the  three  errors, 
combined  in  various  ways,  reappear  as  errors  in  the  spacing 


PRECISION  WORK  AND  WORKMANSHIP  25 

of  the  gear  teeth.  In  some  of  these  positions  the  three  errors 
are  added  together  and  if  the  work  is  continued  long  enough, 
a  position  will  ultimately  be  found  in  which  the  three  maximum 
errors  are  added  together.  These  considerations  show  that  the 
errors  in  the  product  must  exceed  the  individual  errors  of  the 
dividing  head  parts. 

Suppose  next  that  these  gears  are  to  be  the  change  gears  of  a 
lathe  and  assume  them  to  be  mounted  on  the  lathe  for  the 
cutting  of  a  screw.  The  gears  are  first  class  gears  because  they 
were  made  with  first  class  appliances  but,  as  we  have  seen, 
they  contain  errors.  If  the  lathe  is  from  a  high  class  maker  its 
lead  screw  is  a  high  grade  product,  but  again  the  maker  is 
the  last  man  who  would  claim  it  to  be  perfect.  Like  the  divid- 
ing head  parts,  it  contains  errors  that  can  be  found  and  measured. 1 
Under  these  conditions  it  is  plain  that  when  a  screw  is  cut 
in  the  lathe  the  same  combination  and  addition  of  errors  takes 
place,  the  resulting  screw  being  of  an  accuracy  which  is  inferior 
to  that  of  the  lead  screw  of  the  lathe. 

Assume  next  that  this  screw  is  to  be  the  worm  of  the  dividing 
head  of  a  milling  machine.  Assume  it  to  be  in  place  and  a 
second  set  of  gears  to  be  cut.  Then  assume  these  gears  to 
be  placed  on  the  lathe  and  another  worm  to  be  cut  which,  in 
turn,  is  used  to  cut  another  set  of  gears,  and  so  on  indefinitely. 
It  is  clear  that  in  every  case  the  addition  of  enors  takes  place 
and  that  each  succeeding  worm  and  set  of  gears  is  more  in- 
accurate than  its  predecessor.  A  vicious  circle,  so  to  speak, 
has  been  established  and  every  time  we  go  around  it  the  pro- 
duct is  worse  than  the  time  before. 

The  above  is  an  illustration  of  the  degradation  of  work- 
manship from  geometrical  causes.  There  are  other  causes 
which  are  more  universal  and  all-pervading  than  this.  If  a 
bar  be  turned  in  a  lathe  and  then  placed  in  a  grinding  machine 
and  a  light  cut  be  taken  from  it,  the  action  of  the  grinding  wheel 
will  disclose  high  and  low  spots,  precisely  as  the  turning  tool 
in  a  lathe  will  disclose  high  and  low  spots  in  a  bar  of  rough  iron. 
Now  the  errors  thus  disclosed  are  not  in  the  lathe.  The  ways 

1  Methods  of  finding  and  measuring  some  of  these  errors  are  given  on 
later  pages. 


26  METHODS  OF  MACHINE  SHOP  WORK 

of  the  lathe  are  as  straight  as  they  can  be  made  and  the  spindle 
is  as  well  made  and  as  good  a  fit  in  its  bearings  as  can  be  made. 
The  errors  disclosed  by  the  grinding  wheel  are  due  to  the  spring 
of  the  work  under  the  pressure  of  the  cut. 

Other  causes  of  similar  spring  are  found  in  the  pressure  of 
chuck  jaws  and  binding  straps,  while  in  other  cases  the  effect 
of  heat  comes  in  to  introduce  errors.  When  a  gear  blank  is 
mounted  for  cutting  it  is,  at  the  beginning,  of  uniform  tempera- 
ture. The  action  of  the  cutter  generates  heat  and,  after  a  few 
spaces  have  been  cut,  there  exists  a  region  of  gradually  warming 
metal  ahead  of  the  cutter  and  another  of  gradually  cooling  metal 
behind  it,  leading  to  local  distortion  of  the  work. 

It  is  not  to  be  imagined  that  these  errors  are  necessarily 
important  in  their  first  generation.  Some,  like  the  spring  due 
to  binding  straps,  may  be  unless  the  workman  exercises  care 
and  skill,  but  others  are  not.  The  trouble  is,  however,  that, 
like  the  rabbits  in  Australia  and  the  gypsy  moth  in  Massa- 
chusetts, while  harmless  at  first,  they  breed. 

THE  FUNCTION  OF  PRECISION  WORKMANSHIP 

What  is  to  be  done  about  it?  Obviously  something  must  be 
done.  We  cannot  go  on  indefinitely  round  and  round  a  vicious 
circle  repeating  and  multiplying  old  errors.  Some  way  must 
be  found  by  which  to  establish  and  maintain  a  suitable  standard. 
Since  the  workmanship  of  the  product  is  poorer  than  that  of 
the  machine  tools  on  which  it  is  made  and  since  machine  tools 
are  themselves  the  product  of  other  machine  tools,  and  subject 
to  the  same  tendency  toward  degradation,  it  is  plain  that,  if  a 
suitable  standard  is  to  be  maintained,  a  way  must  be  found 
to  offset  this  tendency  and  to  make  machine  tools  better  than 
the  products  that  come  from  them — they  must  be  good  enough 
to  permit  some  letting  down  of  workmanship  and  still  have  the 
workmanship  good  enough  for  its  purpose. 

All  this  is  equivalent  to  saying  that,  back  of  the  commercial 
product,  there  must  be  a  grade  of  workmanship  superior  to  it. 
This  grade  of  workmanship  is  called  precision  workmanship 
and  it  had  its  origin  with  Sir  Joseph  Whitworth.  A  definition 


PRECISION  WORK  AND  WORKMANSHIP  27 

of  precision  workmanship  is  difficult  to  formulate — in  fact  im- 
possible if  it  is  to  be  made  to  cover  all  kinds  of  work  entitled  to 
the  name.  Broadly  speaking  and  with  some  exceptions, 
precision  workmanship  may  be  defined,  in  the  first  place, 
as  workmanship  of  high  accuracy,  of  course,  and,  in  the  second 
place,  as  done  by  methods  of  which  the  resulting  accuracy  is  not 
dependent  on  the  accuracy  of  similar  work  previously  done.1 

Enough  has  been  said  to  show  that  precision  workmanship  is 
of  fundamental  importance  and  it  will  receive  corresponding 
attention  in  these  pages,  the  aim  being  to  give  some  idea  of  its 
spirit,  methods,  and  purposes.  This  can  be  done  by  examples 
only,  as  the  subject  is  not  capable  of  generalization.  The  only 
generalization  regarding  these  methods  that  can  be  made  is  a 
negative  one,  namely:  Precision  work  is  never  done  by 
direct  methods,  those  methods  being,  on  the  contrary,  indirect 
and  roundabout.  Even  this  statement  is  purely  a  matter  of 
observation  which  shows  that  one  practically  never  goes  about  a 
piece  of  precision  work  in  the  manner  which  a  novice  would 
expect  or  as  experience  with  commercial  methods  would 
suggest.  Precision  workmanship  is,  in  fact,  in  a  class  by  itself— 
a  thing  apart. 

It  is  doubtless  already  apparent  that  the  importance  of 
precision  workmanship  is  out  of  all  proportion  to  its  volume. 
Except  as  seen  in  gages,  measuring  machines  and  high-class 
machine  tools,  it  is  not,  to  any  large  extent,  offered  for  sale.  It 
is  usually  done  at  home  to  meet  the  problems  in  hand.  So 
thoroughly  apart  from  ordinary  commercial  workmanship  is  it, 
that  one  may  live  a  life  time  in  a  mechanical  atmosphere  and 
scarcely  see  it.  One  may  go  as  a  common  sightseer  through 
great  factories  which  are  absolutely  dependent  upon  it  and  not 
see  it.  The  National  cash  register,  the  Burroughs  adding 
machine  and  the  Morse  silent  chain  are  composed  chiefly  of 
punchings  which  convey  no  impression  of  accuracy,  and  yet  no 
finer  examples  of  precision  work  exist  than  can  be  found  in  the 
tool  rooms  of  the  factories  where  those  things  are  made.  The 
way  to  see  work  of  this  character  is  to  get  next  to  the  head  tool 
maker  in  a  factory  of  this  kind  and  to  ask  a  few  questions  of  a 

1  The  principal  exception  to  this  definition  is  the  work  of  the  grinding  machine. 


28  METHODS  OF  MACHINE  SHOP  WORK 

kind  to  show  that  the  enquirer  is  one  of  the  elect,  when  the 
result  will  be  to  open  up  such  a  fountain  of  interest  and 
enthusiasm  as  exists  nowhere  else  in  the  factory. 

THE  THREE  KINDS  OF  ACCURACY 

In  discussing  the  subject  of  accuracy  three  kinds  of  accuracy 
are  to  be  distinguished.  These  are  accuracy  of  form,  of  size 
and  of  position  or  adjustment.  By  accuracy  of  position  or 
adjustment  is  not  meant  the  kind  of  adjustment  obtained  with 
a  knurled  headed  screw  but  the  kind  of  adjustment  that  is 
built  into  a  machine.  For  example,  the  head  and  tail  spindles 
of  a  lathe  must  be  accurately  in  line  with  one  another,  the 
movement  of  the  cross  slide  must  be  accurately  at  right  angles 
to  this  line  and,  similarly,  the  shaft  of  a  steam  engine  must  be 
at  right  angles  with  the  center  line  of  the  cylinder,  all  of  these 
cases  being  illustrations  of  what  is  meant  by  the  term  accu- 
racy of  position  or  adjustment. 

Accuracy  of  form  and  of  position  are  equally  important 
whether  machinery  is  made  or  manufactured,  but  accuracy  of 
size  is  of  importance  in  the  manufacturing  system  only.  For 
example,  in  making  the  shaft  of  a  steam  engine  of  which  the 
drawing  calls  for  a  diameter  of  ten  inches,  it  is  obviously  of  no 
importance  whether  the  actual  size  is  exactly  that  or  not  and, 
made  by  the  usual  methods,  it  is  certain  to  vary  from  that  size 
by  several  thousandths  of  an  inch.  It  is  likewise  of  no  import- 
ance whether  or  not  the  shafts  of  different  engines  are  of  ex- 
actly the  same  size.  The  requirements  are  that  the  shaft  shall 
be  round  and  straight — that  is,  have  accuracy  of  form — that  it 
shall  be  a  suitable  fit  in  its  bearings  and  that,  when  assembled, 
it  shall  stand  at  right  angles  with  the  center  line  of  the  cylinder 
— that  is,  have  accuracy  of  position. 

In  manufactured  work,  on  the  other  hand,  accuracy  of  size  be- 
comes important  because  of  the  necessity  for  interchangeability 
and  it  is  because  of  the  necessity  for  interchangeability  in  one 
case  and  the  absence^  of  it  in  the  other  that  we  have  the  dif- 
ferent methods  of  measuring  in  the  two  systems. 

Of  accuracy  of  form  we  have  no  unit,  gage  or  method  of  meas- 


PRECISION  WORK  AND  WORKMANSHIP  29 

urement.  Because  of  this  we  cannot  specify  in  any  definite 
manner  the  degree  of  accuracy  of  form  desired.  Accuracy  of 
this  kind  is  determined  by  the  method  of  production.  If  a 
planed  surface  is  sufficiently  accurate  for  the  purpose  we  call 
for  planing;  if  scraping  is  needed  we  call  for  it  and  if  we  want 
something  better  still  we  call  for  lapping.  In  the  same  way 
turning,  grinding  or  lapping  is  called  for  in  connection  with 
round  work  and  in  accordance  with  the  degree  of  accuracy  re- 
quired. It  does  not  follow  that  all  planed,  scraped,  turned,  ground 
or  lapped  work  is  of  the  same  grade,  but,  in  the  absence  of  any 
definite  unit  of  accuracy  of  form,  specifications  of  the  method 
of  production  are  the  only  recourse,  the  expectation  being  that 
the  work  will  come  up  to  the  standard  of  the  methods  specified. 

THE  ORIGINAL  PRECISION  PROCESS 

The  first  precision  process  to  be  taken  up  is  scraping,  which 
insures  that  surfaces  shall  be  flat — that  is,  have  accuracy  of  form. 
Not  only  is  this  process  the  first  to  be  taken  up  here,  but  it  was 
the  original  precision  process,  as  it  is  still  the  most  important 
and  the  most  common.  It  is,  moreover,  the  foundation  of  all 
others  as  it  is  a  simple  fact  that  not  one  thing  of  a  precision 
character  can  be  done  without  flat  surfaces  to  begin  with.  The 
process  was  invented  by  Whitworth  and,  although  now  a 
commonplace  thing  in  the  shops  it  was,  when  new,  received  and 
published  as  a  paper  by  the  foremost  scientific  society  of  the 
world — The  British  Association  for  the  Advancement  of 
Science.  The  publication  of  this  paper  took  place  in  1840  and 
it  marks  an  epoch  in  the  history  of  the  machine  shop,  as  it 
marks  the  birth  of  the  attainment  of  precision.  Prior  to  that 
date  there  was  no  known  means  of  making  truly  flat  surfaces, 
which  is  equivalent  to  saying  no  known  means  of  doing  precision 
work  of  any  kind. 

The  process  is  believed  to  have  been  brought  to  the  United 
States  by  A.  M.  Freeland  at  a  date  which  cannot  be  located 
more  closely  than  that  it  took  place  prior  to  I857-1 

1  Regarding  this  and  other  features  of  Mr.  Freeland's  work,  of  which  particulars 
are  given  later,  the  author's  information  is  obtained  from  W.  H.  McFaul  who  was 
associated  with  him  from  1857  until  the  end  of  his  life. 


30 


METHODS  OF  MACHINE  SHOP  WORK 


The  ordinary  process  of  scraping,  with  a  standard  surface 
plate  already  in  existence,  is  well  known  and  need  not  be  de- 
scribed. Whitworth's  invention  was  of  a  method  by  which 
plates  were  made  without  reference  to  existing  plates  and  such 
that  the  method  itself  supplied  the  proof  of  the  accuracy  of  the 
result.  In  brief,  the  process  consists  of  making  a  set  of  three 
plates  and  continuing  the  scraping  until  any  two  plates  from  the 
set  of  three  make  perfect  contact  throughout  their  surfaces. 
In  order  to  insure  this  it  is  necessary  that  each  plate  have 
three  points  of  support  and  no  more.  Three  points  determine 
a  plane  and  with  three  points  of  support  a  plate  may  rest  on 
any  surface  without  distortion  due  to  its  own  weight.  With 
more  points  of  support  a  plate,  when  placed  on  a  work  bench, 
which  cannot  be  flat,  will  distort  from  its  own  weight  and, 
placed  in  different  positions  on  the  bench,  it  will  distort  in 


FIG.  5. 


FIG.  6. 


FIG.  7. 


FIG.  8.  FIG.  9. 

Method  of  originating  flat  surfaces. 

different  degrees  and  directions.  Satisfactory  results  cannot 
be  obtained  with  more  than  three  supporting  points.  The 
ribbing  also  should  be  carefully  laid  out  with  the  primary  ribs 
connecting  the  three  supporting  points.  Such  ribs  are  suffi- 
cient for  small  plates,  but  larger  ones  require  additional  ribs. 

The  process  is  illustrated  in  detail  in  Figs.  5-9.  The  plates 
are  first  planed  and  then  one  of  them  is  smeared  with  paint- 
red  lead  or  Prussian  blue.  The  second  plate  is  then  rubbed 
upon  the  first,  after  which  the  high  spots  shown  by  the  paint 
are  removed  with  the  scraper.  This  is  repeated  several  times 
when  the  paint  is  removed  from  the  first  plate  and  ap- 


PRECISION  WORK  AND  WORKMANSHIP  31 

plied  to  the  second  and  the  scraping  process  is  continued  on 
the  first.  The  object  of  reversing  the  paint  is  to  get  rid 
of  the  tooled  surfaces  and  their  local  irregularities.  Even- 
tually the  plates  are  brought  into  agreement  but  without  cer- 
tainty of  their  being  flat — the  presumption  being,  in  the  ratio 
of  infinity  to  one,  that  they  are  not  flat  but  curved  as  in  Fig.  5. 
When  a  satisfactory  degree  of  agreement  has  been  obtained,  one 
of  the  plates,  as  b,  Fig.  5,  is  laid  to  one  side  and  c  is  scraped  to 
agree  with  a  as  in  Fig.  6.  At  this  stage  of  the  work  there  is  no 
reversal  of  the  painting  and  scraping,  the  aim  being  to  make  b 
and  c  duplicates — that  is,  have  the  same  degree  of  untruth. 
When  agreement  between  a  and  c  has  been  obtained  as  in  Fig.  6 
a  is  laid  to  one  side  and  b  is  brought  back  as  in  Fig.  7.  The  de- 
gree of  untruth  of  both  b  and  c  which,  in  the  illustration,  is,  of 
course,  grossly  magnified,  is  made  manifest  by  another  applica- 
tion of  paint  and  the  scraping  process  is  renewed,  the  aim  at  this 
stage  being  to  remove,  as  nearly  as  possible,  the  same  amount 
of  metal  from  each  plate.  To  insure  this  b  is  first  smeared 
with  paint  and  a  certain  number  of  scrapings  are  made  on  c, 
after  which  the  paint  is  applied  to  c  and  the  same  number  of 
scrapings  is  made  on  b.  The  result  is,  obviously,  a  great  im- 
provement, but  when  b  and  c  have  been  brought  to  agreement 
there  is  still  an  overwhelming  probability  that  they  will  still  be 
curved,  although  to  a  much  larger  radius  as  indicated  in  Fig.  8. 
After  agreement  has  again  been  brought  about,  one  of  the  plates, 
as  b,  is  placed  to  one  side  and  a  is  scraped  to  agree  with  c,  Fig.  9. 
When  this  has  been  accomplished  a  and  b  have  become  dupli- 
cates, when  they  are  brought  together  and  scraped  to  agree- 
ment— the  scraping  being  again  divided,  as  nearly  as  possible, 
equally  between  them.  This  process  is  continued  with  pro- 
gressive improvement  until  any  two  of  the  three  plates  show 
perfect  agreement,  when,  by  the  very  nature  of  the  process,  all 
three  of  them  are  flat. 

It  may  be  objected  that  the  process  is  one  of  successive 
approximation  to  which  there  can  be  no  end  but,  as  a  matter  of 
fact,  there  is.  The  process  may  be  compared  with  a  rapidly 
converging  series — meaning  by  this,  not  rapid  in  the  sense  of 
time,  for  the  work  is  slow  and  tedious,  but  rapid  in  the  sense 


32  METHODS  OF  MACHINE  SHOP  WORK 

that,  if  the  work  is  intelligently  done,  Comparatively  few  passes 
around  the  circle  will  bring  the  plates  to  a  condition  in  which 
no  further  error  can  be  discovered. 

It  will  be  observed  that  this  is  a  perfect  illustration  of  the 
definition  of  precision  work,  as  the  result  obtained  is  in  no  way 
dependent  upon  anything  previously  done.  Given  a  scraper 
and  a  pot  of  paint,  it  might,  if  necessary,  be  done  in  the  wilder- 
ness with  just  as  good  final  results  as  if  done  in  the  best  machine 
shop  in  the  world. 

There  is  a  high  degree  of  satisfaction  in  doing  work  of  this 
character.  When  finished,  one  feels  that  he  has  really  made 
something — made  it  himself  and  without  dependence  upon 
others  or  the  work  of  others. 

Plates  made  in  this  manner  are  called  original  plates.  It 
is  not  to  be  understood  that  all  plates  are  original  and,  as  a 
matter  of  fact,  but  few  of  them  are.  With  three  plates  origi- 
nated in  this  manner,  they  may  be  used  as  standards  and  be 
copied  indefinitely,  provided  they  are  occasionally  tested  and 
corrected  by  another  application  of  the  process  by  which  they 
were  made. 

When  long  and  narrow,  surface  plates  become  straight  edges 
and  in  this  form  they  illustrate  Dr.  Sweet's  classical  definition: 
"A  perfect  straight  edge  is  one  of  three,  any  two  of  which, 
when  placed  together,  coincide  throughout  their  length." 
This  is  a  mechanical  definition  of  a  straight  line.  It  is  funda- 
mental and  is  at  least  as  satisfactory  as  any  geometrical  defini- 
tion that  has  ever  been  given. 

APPLICATIONS  OF  SCRAPED  STANDARDS 

One  application  of  such  straight  edges  is  to  the  making  of 
the  V's  and  cross  rails  of  planing  machines  and  this  applica- 
tion is  a  perfect  illustration  of  the  manner  in  which  precision 
workmanship  establishes  a  standard  and  sets  a  limit  to  the 
degradation  of  commercial  workmanship.  Were  the  V's 
and  cross  rails  of  planing  machines  made  on  existing  planing 

1  There  is  no  class  of  work  in  which  good  judgment  on  the  part  of  the  workman 
is  more  important  than  this. 


PRECISION  WORK  AND  WORKMANSHIP  33 

machines  and  were  this  process  repeated  indefinitely,  the 
accumulation  of  errors,  which  has  been  explained,  would  ob- 
viously be  in  full  operation  and  there  would  be  no  limit  to 
the  process  of  degradation.  By  scraping  the  V's  and  cross 
rails,  however,  every  planer  begins  its  life  with  a  certain 
standard  of  accuracy,  and  the  work  which  comes  from  it  is 
only  once  removed  from  precision  workmanship.1 

Figs.  10  and  n  show  the  application  of  a  straight  edge  to 
the  testing  of  the  vertical  parallelism  of  the  ways  of  a  lathe  bed, 
as  practised  at  the  works  of  the  Hendey  Machine  Company. 
Six  blocks  which  are  flat  on  their  tops  and  have  V  notches  to 
fit  the  V's  of  the  lathe  bed,  are  placed  upon  the  V's  and  across 
them  are  laid  three  parallel  strips — all  these  parts  being  ac- 
curately made  so  that,  the  lathe  bed  V's  being  individually 
straight,  the  straight  edge  will  make  contact  with  all  three  of 
the  parallels  in  the  position  shown  in  Fig.  10.  If,  now,  the  lathe 
bed  V's  are  not  parallel  vertically  the  tops  of  the  parallels 
become  three  elements  of  a  warped  surface  containing  no 
straight  lines  except  one  set  parallel  with  the  parallels  and 
another  set  parallel  with  the  lathe  V's.  Consequently,  if  the 
straight  edge  is  swung  diagonally  across  the  lathe  bed  as  in 
Fig.  ii  it  will  ride  upon  the  end  parallels  and  fail  to  make  con- 
tact with  the  center  one,  or  it  will  ride  upon  the  center  one  and 
fail  to  make  contact  with  the  end  ones  and,  the  direction  of 
the  error  being  determined,  the  lathe  bed  V's  may  be  scraped 
to  correct  it. 

Another  application  of  the  same  principle  is  shown  in  Fig.  1 2, 
which  illustrates  the  process  of  erecting  a  long  planer  bed 
in  the  shops  of  the  American  Tool  Works  Company  on  which 
the  work  is  finished  but  which,  by  reason  of  its  length — fifty- 
five  feet — and  flexibility,  must  be  set  in  its  permanent  position 
with  great  care.  The  planer  V's  being  inverted  from  those  of 
the  lathe,  the  V  blocks  used  in  the  former  case  are  here  re- 

1  The  author  is  well  aware  that  some  planer  manufacturers  succeed  in  making 
planer  V's  of  a  satisfactory  degree  of  accuracy  without  scraping  them,  but  this 
does  not  alter  the  fact  that  the  work  was  begun  with  scraped  V's  and  that  the 
scraping  process  must  be  reverted  to  again  from  time  to  time  if  a  suitable  standard 
is  to  be  maintained. 
3 


34 


METHODS  OF  MACHINE  SHOP  WORK 


FIG.  10. — Testing  a  lathe  bed  for  straightness. 


FIG.  ii.— Testing  a  lathe  bed  for  wind. 


PRECISION  WORK  AND  WORKMANSHIP 


35 


placed  by  short  cylinders  which  may  be  easily  made  of  the  same 
diameter.  Across  these  cylinders  are  laid  three  parallels  of 
precisely  the  same  thickness  and  to  these  the  straight  edge  is 
applied  in  the  manner  shown  in  connection  with  the  lathe  bed— 
the  straight  edge  in  this  case  being  eight  feet  long.  Below  the 
planer  bed  at  regular  intervals  adjustable  wedges  are  placed 


FIG.  12. — Erecting  a  long  planer  bed. 

and  by  suitable  adjustment  of  these  in  accordance  with  the 
indications  of  the  spirit  level  shown  and  of  the  straight  edge, 
the  planer  bed  may  be  brought  to  a  position  in  which  it  is  level 
and  without  wind. 


ORIGINATING  SQUARES  BY  THE  SCRAPING  PROCESS 

Other  things  besides  surface  plates  and  straight  edges  may 
be  originated  by  the  scraping  process  and  among  these  are 


36 


METHODS  OF  MACHINE  SHOP  WORK 


right  angles  or  squares.  The  customary  form  of  shop  square  is 
not  satisfactory.  The  surface  of  the  blade  edge  is  inadequate 
and  the  blade  is  not  well  secured  in  the  head.  Few  shop  squares 
which  have  seen  much  use  will  satisfactorily  stand  a  test  for 
accuracy. 

Figs.  13-16  show  a  form  of  square  due  to  Dr.  John  E.  Sweet 
which  is  far  more  permanent  than  the  usual  form.     The  hy- 


FIG.  13. 


FIG.  14. 


FIG.  15.  FIG.  1 6. 

A  superior  machine  shop  square. 

pothenuse  and  other  braces  insure  that,  once  made  correct,  it 
will  stay  so,  while  the  surfaces  are  large  enough  to  endure 
much  use  without  appreciable  wear.  The  hypothenuse  gives 
angles  of  thirty  and  sixty  degrees  and  the  short  brace  has  raised 
pads  near  its  ends  by  which  angles  of  forty-five  degrees  may  be 
determined.  Small  plates,  slightly  longer  than  the  width  of 
the  faces  of  the  square  and  shown  each  side  the  square  in  Fig. 


PRECISION  WORK  AND  WORKMANSHIP 


37 


13,  are  fitted  with  small  bolts  and  thumb  nuts  by  which  they 
may  be  attached  to  the  square  as  indicated  in  the  various  figures. 
Fig.  15  shows  the  instrument  in  use  for  obtaining  a  right  angle, 
Fig.  14  for  obtaining  angles  of  forty-five  degrees,  and  Fig.  16 
for  obtaining  angles  of  thirty  and  sixty  degrees. 

The  method  of  originating  these  squares — which  was  used  by 
Whitworth — is  shown  in  Figs.  17-19.  A  straight  edge  is  first 
provided  and  here  we  have  an  illustration  of  the  fundamental 
importance  of  straight  surfaces  for,  without  them,  the  originat- 
ing of  the  squares  would  be  impossible.  As  in  the  case  of  the 
surface  plates  and  straight  edges  the  squares  are  made  in  sets  of 
three.  These  are  first  planed  as  correctly  as  possible  and,  as  in 
the  case  of  the  surface  plates,  two  of  them  are  first  scraped  to 
make  their  sum  equal  to  two  right  angles  but,  as  indicated  in 
Fig.  17,  when  this  has  been  done  the  probabilities  are  all 


FIG.  17.  FIG.  18. 

First  method  of  originating  squares. 


FIG.  19. 


against  their  being  true  squares,  one  of  them  being  slightly  over 
and  the  other  slightly  under  ninety  degrees.  When  agreement 
has  been  secured,  one  of  the  squares,  as  &,is  removed  and  square 
c  is  substituted  for  it  and  scraped  to  agree  with  a — no  scraping 
being  done  on  a  at  this  stage  in  order  to  insure  that  b  and  c  shall 
have  the  same  degree  of  untruth.  When  the  agreement  be- 
tween a  and  c  is  obtained,  as  indicated  in  Fig.  18,  a  is  removed 
and  b  and  c  are  placed  together  as  in  Fig.  19,  when  they  are 
scraped  into  agreement,  the  aim  at  this  stage  being,  as  in  the 
case  of  the  surface  plates,  to  divide  the  scraping  equally  between 
the  two  squares  as  nearly  as  can  be  done.  The  result  is  a  large 
improvement,  but  when  b  and  c  have  been  brought  to  agreement 
there  will  still  be  an  error  similar  to  that  between  a  and  b  in 
Fig.  17  but  smaller.  The  process  of  correcting  this  is  exactly 


38  METHODS  OF  MACHINE  SHOP  WORK 

parallel  with  that  followed  in  the  case  of  the  surface  plates 
and  it  seems  unnecessary  to  explain  it  in  detail  at  greater  length. 
The  final  result  is  three  squares  which,  by  the  nature  of  the 
process  by  which  they  were  made,  are  known  to  be  correct. 
Uses  of  such  squares  are  shown  in  Figs.  82-85. 

OTHER  METHODS  OF  ORIGINATING  SQUARES 

Other  methods  exist  for  originating  squares,  one  of  which  is 
illustrated  in  Fig.  20.  A  square — in  this  case  having  an  in- 
ternal angle — is  first  made  as  accurately  as  possible  by  mechani- 
cal means.  A  rectangular  plate  of  sheet  metal  is  then  fitted  to 
this  square  at  one  of  its  angles,  as  a,  and  then  at  b  and  c  in  order. 


FIG.  20. — Second  method  of  originating  squares. 

This  done,  the  square  is  applied  to  the  angle  at  d  when  the  error 
will  be  shown  at  e  multiplied  by  four — three  times  for  the 
rectangular  plate  and  once  for  the  square.  The  direction  of  the 
error  being  now  known,  the  square  is  corrected,  as  nearly  as  may 
be,  and  the  angles  of  the  plate  are  corrected  to  agreement  with 
it.  The  process  is  continued  until  the  error  at  e  disappears 
when,  obviously,  both  the  square  and  the  plate  are  correct. 
The  work  once  done,  the  square  may  be  put  into  use  and  the 
plate  may  be  preserved  for  making  future  squares. 

In  the  above  cases  the  original  squares  were  intended  for 
shop  use.     More  frequently  the  aim  is  to  make  a  test  square  by 


PRECISION  WORK  AND  WORKMANSHIP 


39 


which  to  test  and  correct  the  working  squares.  An  example  of 
this  kind,  from  the  works  of  the  Ingersoll  Milling  Machine  Com- 
pany, is  shown  in  Fig.  21.  A  scraped  surface  plate  of  suitable 
form  is  first  made  and  then  a  skeleton  cylinder  is  ground  on  a 
grinding  machine  to  be  truly  parallel  and  cylindrical  and  to 


FIG.  21. — Third  method  of  originating  squares. 

have  at  least  one  end  truly  square  with  its  center  line — the 
making  of  such  a  cylinder  with  a  good  grinding  machine  being 
an  easy  and  simple  matter.  The  cylinder  is  then  placed  upon 
the  surface  plate  as  shown  when,  by  the  nature  of  the  work, 
the  angle  between  the  surface  plate  and  the  side  of  the  cylinder 
is  truly  square.  The  illustration  shows  also  the  manner  of  test- 


40 


METHODS  OF  MACHINE  SHOP  WORK 


FIGS.  22  and  23. — Fourth  method  of  originating  squares. 


PRECISION  WORK  AND  WORKMANSHIP  41 

ing  shop  squares  by  the  test  square.  Placed  in  position  as 
shown,  small  pieces  of  paper  are  placed  between  the  cylinder 
and  the  blade  of  the  shop  square  and,  if  the  pieces  of  paper 
are  all  pinched  alike,  the  truth  of  the  shop  square  is  proven. 

Pieces  of  paper  used  in  this  way  are  commonly  called  tissues, 
although  actual  tissue  paper  is  seldom  or  never  used.  Good 
printing  paper  is  surprisingly  uniform  in  thickness  and,  in  use, 
is  very  sensitive  and  satisfactory.  It  has  many  applications. 

It  will  be  observed  that  this  process  does  not  conform  to  the 
definition  of  precision  work,  as  the  result  depends  on  the  ac- 
curacy of  the  grinding  machine.  It  is  the  cheapest  method  of 
making  a  correct  square  and  is  in  wide  use. 

Another  form  of  test  square,  from  the  works  of  Ludwig  Loewe 
and  Company,  is  shown  in  Figs.  22  and  23. l  The  base  of 
the  instrument  is  a  narrow  surface  plate  having  at  its  rear  a 
vertical  arm  from  which  there  is  suspended  a  blade  of  hardened 
steel  of  which  the  two  edges  are  truly  parallel.  In  use,  the  shop 
square  resting  upon  the  surface  plate  has  its  blade  applied  to  the 
blade  of  the  instrument  as  indicated  in  the  dotted  outline  of  the 
plan  view.  The  instrument  blade  is  now  adjusted  to  make  con- 
tact with  the  blade  of  the  shop  square  and  the  shop  square  is 
turned  bodily  around  and  applied  to  the,  opposite  edge  of  the 
instrument  blade.  If  the  shop  square  is  correct,  it  will,  of  course, 
make  perfect  contact  in  the  second  position  whereas,  if  in- 
correct, the  error  will  appear,  multiplied  by  two,  as  an  angle 
between  the  two  blades.  To  facilitate  the  use  of  the  instrument, 
long  narrow  mirrors  a  and  b  are  placed  as  shown,  together  with  a 
row  of  incandescent  lights  c  and  a  suitable  shield  d — the  instru- 
ment being  used  in  a  darkened  room. 

Another  very  satisfactory  form  of  square  for  some  purposes 
is  an  application  of  the  spirit  level.  A  false  impression  of  the 
accuracy  of  this  instrument  prevails  because,  in  the  form  most 
commonly  seen — that  used  by  masons  and  carpenters — it 
makes  no  pretension  to  accuracy.  For  this  use,  in  fact,  a  really 
accurate  level  would  be  practically  useless.  Every  surveying 
instrument  carries  precision  levels  and  should  prevent  the 

1  The  two  illustrations  do  not  agree  in  all  details  because  made  from  different 
instruments.  They  are,  however,  identical  in  all  essentials. 


42 


METHODS  OF  MACHINE  SHOP  WORK 


formation  of  this  impression.     In  the  present  use  the  level  used 
is  of  surveying-instrument  grade. 

A  shop  square  in  which  dependence  is  place  upon  a  spirit 
level  is  shown  in  use  in  Fig.  24,  the  operation  being  that  of  testing 
the  squareness  of  a  boring  mill  housing  with  its  bed.  The 
application  of  the  instrument  is  obvious  and  self-explanatory. 


FIG.  24.- — The  spirit  level  square. 

ORIGINATING  ANGLES  OTHER  THAN  RIGHT  ANGLES  BY  THE 
SCRAPING  PROCESS 

Certain  angles  other  than  right  angles  may  be  originated  by 
the  scraping  process  and  among  these  are  angles  of  forty-five 
degrees  for  which  the  process  is  indicated  in  Fig.  25.  As 
always,  we  begin  with  a  surface  plate  to  which  must  be  added 
two  straight  edges.  In  order  to  originate  angles  of  forty-five 
degrees  we  must  first  have,  also,  a  right  angle  as  one  angle  of  a 
triangle  of  which  the  forty-five-degree  angles  desired  are  the 
others.  The  straight  edges  are  laid  upon  the  surface  plate  and 
adjusted  to  fit  one  of  the  forty-five-degree  angles,  a,  of  the 


PRECISION  WORK  AND  WORKMANSHIP 


43 


square.  The  square  is  then  removed  and,  without  disturbing 
the  straight  edges,  it  is  replaced  with  the  angle  b  in  the  angle 
between  the  straight  edges.  The  angle  c  being  already  a  right 
angle,  if  the  test  shows  angles  a  and  b  to  be  equal,  they  are 
necessarily  of  forty-five  degrees  and  if  they  are  unequal,  the 
direction  in  which  scraping  must  be  done  on  the  hypothenuse 
in  order  to  make  them  equal  will  be  shown  by  the  tests. 

Angles  of  thirty  and  sixty  degrees  may  also  be  originated  in 
sets  of  three.  For  this  we  require  a  straight  edge,  a  square  and 
three  triangles  of  which  the  right  angles  are  correct  and  of  which 
the  other  angles  are  to  be  the  ones  required. 

With  these  parts  provided,  they  are  grouped  in  the  manner 
shown  in  Fig.  26  and  the 
triangles  are  scraped  until 
the  right  angle  between 
the  stright  edge  and  the 
square  is  filled  by  the  two 
angles  of  the  triangles. 
When  doing  this  the  scrap- 
ing of  each  triangle  is  on 
its  hypothenuse  alone  in 


FIG.    25. — Originating  angles  of  forty-five 
degrees. 


order  to  avoid  disturbing 
the  correctness  of  its  right 
angle.  When  the  right 

angle  between  square  and  straight  edge  is  completely  filled, 
the  top  and  bottom  lines  of  the  triangles  are  truly  parallel 
because  of  the  correctness  of  the  right  angles,  and  we  have  two 
parallel  lines  cut  by  a  diagonal.  Consequently  angles  a  and  b 
are  equal,  as  are  c  and  d.  Moreover  a  and  c  are  complements, 
as  are  b  and  d.  There  is,  however,  no  certainty  that  a  and  b 
are  truly  thirty  degrees  or  that  c  and  d  are  truly  sixty  degrees 
and,  without  the  certainty  that  they  are  correct,  there  is  every 
probability  that  they  are  wrong.  Triangle  A  is  now  removed 
and  triangle  C  is  substituted  for  it  and  scraped  on  its  hypothe- 
nuse until  the  right  angle  is  again  filled — no  scraping  being  done 
on  triangle  B  at  this  stage,  as  the  aim  is  to  insure  that  the  three 
triangles  have  the  same  degree  of  untruth.  This  process 
completed,  we  know  that  the  three  smaller  angles,  while  in  all 


44 


METHODS  OF  MACHINE  SHOP  WORK 


probability  not  of  thirty  degrees,  are,  nevertheless,  €qual. 
They  are  next  grouped  as  shown  in  Fig.  27  when  the  error,  multi- 
plied by  three,  is  at  once  shown  by  the  three  angles  added 
together  failing  to  fill,  or  more  than  filling,  the  right  angle.  The 
direction  of  the  error  being  shown,  the  three  triangles  are  scraped 
by  the  same  amount,  as  nearly  as  possible,  and  each  upon  its 
hypothenuse,  until  the  right  angle  of  Fig.  27  is  perfectly  filled. 
In  spite  of  the  care  used,  this  scraping  will,  in  all  probability, 
slightly  disturb  the  equality  of  the  angles,  and  the  triangles  are 


FIG.  26. 


FIG.  27. 


FIG.  28. 
Originating  angles  of  thirty  and  sixty  degrees. 

then  grouped  again  as  in  Fig.  26  and  the  error  is  corrected 
by  a  second  application  of  the  first  process.  This  process  is 
repeated  until  the  triangles  satisfy  both  tests  when,  the  angles 
being  equal  and  their  sum  ninety  degrees,  they  are  necessarily 
correct. 

Two  of  the  angles  of  each  triangle  being  now  known  to  be  of 
ninety  and  thirty,  it  follows  that  the  third  one  must  be  of  sixty 
degrees  but,  if  desired,  an  independent  test  of  this  fact  may  be 
made  by  grouping  the  triangles  as  shown  in  Fig.  28  and,  should 


PRECISION  WORK  AND  WORKMANSHIP 


45 


they  satisfy  the  test,  the  correctness  of  the  sixty-degree  angles 
is  obviously  proven. 

OTHER  METHODS  OF  ORIGINATING  ANGLES 

There  is  in  the  machine  shop  a  surprising  lack  of  appliances 
for  making  pieces  of  which  the  surfaces  are  to  have  various 
angles  with  one  another.  Universal  milling  machines  are,  of 
course,  supplied  with  protractors  but  these  are  never  fitted 
with  verniers  and  can  only  be  read  with  accuracy  for  the  angles 
which  actually  appear  in  the  graduations. 


FIG.  29. — Two-disc  method  of  originating  angles. 

In  the  absence  of  provisions  of  this  sort,  when  correct  angles 
are  required  other  than  those  supplied  by  the  milling  machine 
protractors,  it  is  necessary  to  resort  to  various  expedients. 
One  such  expedient  is  shown  in  Fig.  29,  which  shows  a  surface- 
grinding  machine  fitted  for  producing  a  correct  angle  on  the 
inclined  piece  below  the  grinding  wheel.  This  piece  is  shown 
clamped  to  a  plate  which,  in  turn,  rests  upon  the  magnetic 
chuck  of  the  grinding  machine.  The  plate  has  two  holes 
through  it,  the  centers  of  which  are  at  exactly  the  same  distance 
from  its  bottom  and  which  are  at  a  known  distance  apart. 
Two  discs,  as  shown,  are  made  of  different  diameters  and  with 
short  shanks  which  fit  the  holes  in  the  plate.  It  is  obviously 


METHODS  OF  MACHINE  SHOP  WORK 


a  simple  matter  to  calculate  and  to  make  the  discs  of  such  diam- 
eters that  the  angle  between  their  common  tangent  and  the 
center  line  shall  be  the  angle  required  and,  with  the  piece  of 
work  clamped  in  the  position  shown,  the  result  of  the  grinding  is 
to  produce  this  angle  upon  it. 

This  is  called  the  two-disc  method  and  it  has  many  applica- 
tions and  variations.  More  commonly  it  is  so  used  that  the 
angle  produced  is  that  between  the  two  common  tangents  of 
the  discs  and  not  as  in  the  case  shown,  that  between  one  common 
tangent  and  the  center  line. 

An  application  of  this  kind  is  shown  in  Fig.  30  in  which 
the  piece  a  is  required  to  have  an  angle  of  18  deg.  46  min.  as 


FIG.  30. — Second  application  of  the  two  disc  method  of  originating  angles. 

shown.  The  body  b  of  the  fixture  has  a  tongue  c  fitting  the 
T  slot  of  the  planer  or  milling  machine  table  and  a  ledge  d 
to  act  as  an  abutment  to  the  discs  e  and  /,  the  distance  be- 
tween which  is  determined  by  the  distance  piece  g.  The  piece 
of  work  is  drawn  snugly  against  the  discs  by  the  bridle  k  and 
the  set  screw  j,  a  similar  set  screw  h  securing  the  larger  disc 
in  position  against  the  displacing  tendency  of  the  pressure  of 
the  piece  a  against  it. 

Again,  as  before,  it  is  a  simple  matter  to  calculate  and  to  make 
the  discs  of  proper  diameters  and  the  distance  piece  of  proper 
length  for  the  angle  required  and  then  to  produce  that  angle  on 
the  planer  or  milling  machine  by  planing  or  milling  the  lower 
edge  of  piece  a. 


PRECISION  WORK  AND  WORKMANSHIP 


47 


There  are  in  the  machine  shop  certain  standard  tapers. 
The  taper  shanks  of  twist  drills  and  the  sockets  by  which  they  are 
held  and  driven  are  made  to  the  Morse  taper  of  nominally, 
though  not  exactly,  five-eighths  of  an  inch  per  foot.  The  work 
ends  of  milling-machine  spindles  have  each  a  hole  for  the  cutter 
arbors  made  to  the  Brown  and  Sharpe  taper  of  one-half  inch 
per  foot  and  in  some  other  machine  spindles  the  Sellers  taper  of 
three-quarters  of  an  inch  per  foot  will  be  found.  It  would 


FIG.  31. — Third  application  of  the  two-disc  method  of  originating  angles. 

be  much  better  if  we  had  but  one  taper,  but  the  unfortunate 
diversity  is  too  firmly  established  to  be  corrected. 

Interchangeability  of  these  taper  pieces  in  imperative. 
Twist  drills  must  interchange  in  their  sockets  and  so  with  mill- 
ing-machine arbors.  That  each  milling  machine  should  have 
its  own  complete  set  of  arbors,  for  example,  is  unthinkable. 
Means  for  originating  these  tapers  are  therefore  important, 
both  for  the  original  production  of  plug  gages  by  which  to  test 
them  and  for  the  detection  and  correction  of  wear  of  the 
plug  gages. 

This  may  be  done  by  another  application  of  the  two-disc 


48 


METHODS  OF  MACHINE  SHOP  WORK 


PRECISION  WORK  AND  WORKMANSHIP  49 

method  shown  in  Fig.  31,  which  illustrates  the  originating  of  a 
taper  test  gage  from  which  to  make  the  working  taper  plug 
gage  shown  in  the  background.  The  stand  at  the  left  has  a 
slot  through  it  and  suitable  binding  straps  by  which  to  hold 
the  blades  shown  behind  them,  which  are  adjusted  to  correct 
position  by  means  of  the  parts  shown  in  the  right  foreground. 
These  parts  consist  of  a  steel  block  to  which  are  secured  two 
discs  of  such  size  and  distance  apart  that  the  angle  between 
their  common  tangents  is  the  angle  desired.  The  block  is 
placed  in  the  opening  through  the  stand  from  behind,  the  dimen- 
sions being  such  that  when  thus  placed  the  discs  project  through 
the  stand.  With  the  parts  thus  placed,  the  blades  are  adjusted 
to  contact  with  the  discs,  when,  the  block  and  discs  being  with- 
drawn, we  have  a  gage  with  which  to  compare  the  taper  plug. 

Another  method  of  originating  angles  is  by  the  use  of  the 
sine  bar  (due  to  H.  P.  Camp)  shown  in  Fig.  32.  Here  we  have 
the  work  table  of  a  surface-grinding  machine  on  which  is  placed 
a  swiveled  magnetic  chuck  which  it  is  desired  to  adjust  to  an 
angle  such  that  the  wedge  shown  in  the  foreground  on  the  work 
table  may  be  ground  upon  it  and  with  a  high  degree  of  accuracy. 

The  sine  bar  shown  upon  the  chuck  is  a  bar  of  steel  having 
its  two  edges  accurately  parallel  and  carrying  near  its  ends  two 
pins  of  exactly  the  same  diameter  located  on  a  center  line  which 
is  exactly  parallel  with  the  edges  of  the  strip  and  which  are  at  a 
known  distance  apart — usually  ten  inches  between  centers. 
At  the  right  is  seen  a  height  gage,1  which  is  an  accurate  in- 
strument for  measuring  vertical  distances  from  the  bottom 
of  its  base  to  the  lower  side  of  the  projecting-  finger.  The  sine 
of  the  required  angle  is  taken  from  a  table  and  multiplied  by  the 
distance  between  the  centers  of  the  pins,  when  the  chuck  is 
adjusted  on  its  trunnions  by  trial  until  the  pin  at  the  right 
stands  above  the  pin  at  the  left  by  an  amount  equal  to  the  sine 
of  the  angle  thus  multiplied — this  difference  in  height  being 
determined  by  the  height  gage. 

The  sine  bar  has  many  other  application's  'of  which  two  are 
shown  in  Figs.  33  and  34.  In  Fig.  33  the  bar  is  applied  to  an 

1  This  instrument  is  described  at  greater  length  in  the  chapter  on  Measures 
of  Length. 
4 


50 


METHODS  OF  MACHINE  SHOP  WORK 


angle  plate  and  it  locates  directly  the  piece  of  work  to  be  ground 
to  the  desired  angle.  In  Fig.  34  two  sine  bars  and  a  suitable 
stand  are  so  assembled  as  to  provide  a  taper  gage  similar  to  the 


FIG.  34. — Third  application  of  the  sine  bar  method  of  originating  angles. 

one  already  shown  in  Fig.  31 — the  gage  being  here  shown  in 
the  act  of  gaging  a  taper  reamer. 

The  sine  bar  provides,  perhaps,  the  most  generally  useful 
method  of  originating  angles.     It  is  extremely  simple,  quite 


FIG.  35. — Adjustable  angle  plate  for  originating  angles. 

accurate  and,  unlike  the  two-disc  method,  does  not  require 
special  construction  for  each  case.  Against  it  is  the  fact  that, 
in  each  of  the  repeated  trials  necessary  to  adjust  it,  the  positions 
of  both  pins  are  naturally  disturbed  and  this  adds  to  the  time 


PRECISION  WORK  AND  WORKMANSHIP 


51 


required  for  the  adjustment.  This  may  be  avoided  by  the  angle 
plate  shown  in  Fig.  35  from  the  works  of  the  United  Shoe 
Machinery  Company.  In  this  instrument  one  of  the  pins  is 
concentric  with  the  axis  on  which  the  adjustable  plate  swivels, 
the  result  being  that  the  height  of  the  second  pin  may  be 
adjusted,  once  for  all,  by  the  use  of  the  height  gage  as  shown. 


ORIGINATING  INDEX  PLATES 


The  next  method,  shown  in  Figs.  36-38,  is  from  the  works 
of  the  Westinghouse  Electric  and  Manufacturing  Company  and 
is  for  much  larger  work.  It  was  developed  under  the  following 
conditions: 


FIG.  36. — A  large  index  plate. 

The  magnetic  circuits  of  electric  generators  and  motors  are 
built  up  of  punchings  of  sheet  steel.  In  small  machines  these 
punchings  are  complete  rings  but,  as  the  size  increases,  it  soon 
becomes  impracticable  to  follow  this  plan  and  the  rings  are  made 
of  segments.  Under  these  circumstances  it  becomes  necessary 
to  anchor  the  punchings  to  the  spider  which  carries  them  and 
this  is  done  by  dovetails  which  project  from  the  inner  arcs  of  the 


52 


METHODS     OF  MACHINE  SHOP  WORK 


FIG.  37. — Second  method  of  using  the  large  index  plate. 


FIG.  38. — Divisions  of  the  large  index  plate. 


PRECISION  WORK  AND  WORKMANSHIP  53 

punchings  and  fit  corresponding  dovetail  slots  in  the  spider. 
The  dovetails  must  really  fit  the  slots  because,  not  only  is  it 
necessary  that  the  segments  be  anchored  to  prevent  flying  off  by 
centrifugal  force,  but  they  must  be  so  perfectly  anchored  as  to 
prevent  movement  among  themselves,  as  such  movement  would 
soon  chafe  and  destroy  the  insulation  of  the  windings. 

All  this  requires  that  the  spacing  of  the  dovetails  and  of  the 
dovetail  slots  shall  be  accurate,  and  the  more  so  because,  in 
order  to  preserve  magnetic  continuity,  the  punchings  are  so  as- 
sembled on  the  spider  as  to  break  joints,  the  result  being  that  in 
the  assembling  of  the  punchings  the  dovetails  are  placed  in  the 
slots  in  every  possible  position  around  the  circle.  It  is  clear 
that,  if  good  fits  are  to  be  made  with  uneven  spacing  of  the 
dovetails  and  slots,  the  assembling  would  be  accompanied  by  a 
large  amount  of  hand  fitting.  Formerly  this  was  the  case  and, 
since  a  single  large  armature  contains  many  thousands  of  punch- 
ings, the  cost  of  this  fitting  became  a  serious  item.  To  reduce 
this  cost  the  index  plate  shown  in  Figs.  36-38  was  constructed, 
its  object  being  to  insure  accurate  spacing  of  the  slots  in  the 
spider,  or  of  the  ring  frame  as  the  case  may  be.  The  result  was 
to  reduce  the  time  required  for  the  assembling  to  one-tenth  of 
the  former  figure,  the  case  being  a  perfect  illustration  of  the 
statement  already  made  regarding  the  economy  of  assembling 
due  to  good  workmanship. 

The  index  plate,  which  is  of  fourteen  feet  diameter,  is  shown 
in  Fig.  36  with  an  armature  spider  mounted  upon  it.  The  plate 
is  mounted  upon  a  slotted  cast-iron  floor  plate  and,  as  the  work 
which  it  carries  frequently  weighs  many  tons,  it  is  supported  on  a 
ball  bearing  and  fitted  with  an  electric  motor  shown  in  the  fore- 
ground for  turning  it,  with  hand  adjustment  for  the  final  setting. 
The  slotting  machine  which  is  to  machine  the  dovetail  slots  is 
also  mounted  upon  the  floor  plate,  or,  in  case  the  slots  are  to  be 
on  the  inner  circumference  of  a  ring  frame,  this  frame  is  mounted 
upon  blocks  which  surround  the  index  plate  and  the  slotting 
machine  is  placed  upon  the  index  plate  as  shown  in  Fig.  37. 

Fig.  38  shows  a  near  view  of  the  index  plate.  Several  circles 
are  turned  upon  it,  each  circle  containing  a  number  of  brass  plugs 
in  accordance  with  the  number  of  divisions  to  be  made,  and 


54  METHODS  OF  MACHINE  SHOP  WORK 

upon  these  brass  plugs  fine  lines  are  engraved,  the  turning  of  the 
plate  from  line  to  line  being  determined  by  matching  these  lines 
against  a  stationary  line  on  the  curved  shield  in  front  of  the 
plate.  In  the  case  shown,  this  shield  is  provided  with  a  vernier 
for  more  minute  divisions.1 

This  plate  was  divided  by  means  of  a  high- class  shop  transit 
instrument  which  was  mounted  upon  a  cast-iron  support  whose 
concentricity  with  the  plate  was  insured  by  a  shallow  recess 
turned  in  the  center  of  the  plate  when  the  plate  was  made  and 
shown  in  Fig.  36- — a  projecting  hub  on  the  bottom  of  the  transit 
support  fitting  this  recess.  The  graduated  circle  of  the  transit 
was  of  the  highest  attainable  precision  but,  for  this  purpose,  its 
divisions  were  not  trusted  because,  small  as  its  errors  were,  the 
greatly  increased  radius  of  the  table  over  that  of  the  instrument 
circle  would  have  led  to  a  magnification  of  those  errors  which  it 
was  desired  to  avoid. 

At  a  distance  of  approximately  a  hundred  feet  a  pair  of  tar- 
gets was  erected,  consisting  of  a  horizontal  plank  with  an  ivory 
marker  mounted  on  each  end.  One  of  these  markers  was  fixed 
in  position  while  the  other  was  adjustable  by  a  micrometer 
screw.  The  required  number  of  divisions  in  a  circle  having 
been  reduced  to  degrees  and  minutes,  it  was  easy,  by  swinging 
the  instrument  through  this  angle,  so  to  locate  the  movable 
target  that  the  lines  upon  the  targets  should  be  split  by  the 
cross  hairs  of  the  telescope  at  the  two  positions  defining  this 
angle.  This  done,  the  micrometer  reading  was  taken,  when  the 
setting  was  destroyed,  the  table  was  turned  to  a  new  position, 
and  the  process  repeated  on  a  different  portion  of  the  instru- 
ment circle,  in  order  to  eliminate  local  errors  which  it  might 
contain.  At  each  repetition  the  micrometer  reading  was  taken 
and  when  a  sufficient  number  had  accumulated,  the  average  of 
all  the  readings  was  taken.  The  micrometer  was  then  set  to 
this  average  reading  and  the  dividing  of  the  table  was  done  by 
the  use  of  the  targets  and  without  again  consulting  the  instru- 
ment circle.  In  doing  this,  the  instrument  was  first  adjusted 

1  The  lines  shown  upon  the  edge  of  the  plate  leading  to  the  brass  plugs  are  mere 
leader  lines  to  locate  the  plugs.  The  actual  division  lines  on  the  plugs  are  too 
fine  to  be  seen. 


PRECISION  WORK  AND  WORKMANSHIP  55 

until  its  cross  hair  split  the  line  upon  one  of  the  targets,  when 
table  and  instrument  together  were  turned  until  the  telescope 
cross  hair  split  the  line  upon  the  other  target.  With  the  table 
in  this  position  the  instrument  was  then  turned  back  to  the 
first  target  when  table  and  instrument  together  were  again  re- 
volved to  the  second  target.  At  the  completion  of  each  step 
a  line  was  drawn  on  one  of  the  brass  plugs  and  from  a  fixed 
base,  and  the  process  was  continued  until  the  circle  was  com- 
pleted. In  order  to  avoid  the  effect  of  vibrations  due  to  the 
work  in  progress  in  the  shop,  this  process  was  carried  out  on 
Sunday. 

This  great  index  plate  opens  up  the  subject  of  index  plates 
in  general.  The  process  described  is,  to  the  best  of  the  author's 
knowledge,  unique,  in  that  the  value  of  a  division  of  the  plate 
was  reduced  to  degrees  and  minutes.  The  usual  method  of 
attacking  this  problem  is  to  provide  a  means  by  which  the 
equality  of  the  divisions  is  insured  and  then,  the  number  of 
divisions  being  correct,  the  work  is  necessarily  correct.  As  in 
the  case  of  the  Westinghouse  plate,  precision  methods  are  not 
resorted  to  in  these  matters  in  the  cultivation  of  a  fad  or  the 
pursuit  of  an  ideal.  Such  work  is  done  because  it  is  necessary 
and  this  necessity  sometimes  arises  in  connection  with  work 
for  which  it  would  be  least  expected. 

The  web  printing  press  by  which  newspapers  are  printed 
from  continuous  sheets  does  the  poorest  grade  of  commercial 
printing  and,  at  first  sight,  it  is  the  last  printing  press  in  which 
precision  work  would  be  looked  for.  Between  the  beginning 
and  the  end  of  the  printing  process  there  are,  in  one  of  these 
presses,  about  seventy-five  lineal  feet  of  paper  included,  this 
paper  going  over  and  around  various  cylinders  and  drums  in  its 
progress  through  the  press.  It  is  very  clear  that  unless  these 
cylinders  revolve  at  uniform  velocity  the  effect  on  the  paper 
would  be  disastrous,  and  so  exacting  is  this  requirement  that, 
for  the  production  of  the  gears  which  drive  these  cylinders,  the 
firm  of  R.  Hoe  and  Company  found  it  necessary  to  make  an 
original  index  plate  on  which  more  money  was  probably  spent 
than  on  any  other  existing  index  plate. 


56 


METHODS  OF  MACHINE  SHOP  WORK 


THE  DIVISION  OF  FUNCTIONS 


Before  proceeding  with  the  division  of  index  plates,  one 
feature  of  them  should  be  noticed.  This  relates  to  the  shape 
of  the  indexing  notch  by  which  the  plate  is  located  in  its  various 
positions.  The  correct  shape  of  these  notches  and  of  the 
latch  bolt  which  engages  them  is  shown  in  Fig.  39. 1  The 
natural  and  formerly  the  universal  form  of  the  notches  is  that 
of  a  truncated  V  as  shown  in  Fig.  40. .  In  the  operating  of  an 
index  plate  the  latch  bolt  must  be  depended  upon  to  move 


FIG.  39.  FIG.  40. 

Correct  and  incorrect  constructions  of  index  rings. 

the  plate  a  small  distance  as  it  enters  the  notch.  In  other 
words,  the  sides  of  the  truncated  V  notch  are  subject  to  wear 
which  in  time  destroys  its  accuracy.  In  the  notch  shown  in 
Fig.  39,  one  side  will  be  observed  to  be  radial  while  the  opposite 
side  is  inclined  to  the  radius  and  the  latch  bolt  is  offset,  one 
edge,  prolonged,  passing  through  the  center  of  the  ring.  Under 
these  circumstances  the  radial  side  cannot  produce  movement 
and,  the  turning  mechanism  being  so  adjusted  as  to  leave  the 
plate  in  a  position  such  that  the  bolt  will  enter  the  notch,  it  is 
clear  that  the  inclined  side  alone  can  do  the  final  turning,  the 
wear  due  to  this  work  being  thus  confined  to  this  side,  while 
the  accuracy  of  the  radial  side  remains  unimpaired  for  a 
long  period.  The  only  result  of  wear  is  that  the  depth  by 

1  This  construction  was  introduced  into  general  practice  by  Pratt  and  Whitney. 
In  a  letter  published  in  the  American  Machinist  for  Oct.  13,  1898,  Mr.  Pratt 
disclaims  its  invention,  saying  that  he  obtained  it  from  Colt's  Armory. 


PRECISION  WORK  AND  WORKMANSHIP  57 

which  the  bolt  enters  the  notch  gradually  increases  but  this 
does  not  affect  the  accuracy  of  the  indexing.  With  the  V 
notch,  both  sides  are  equally  concerned  in  the  final  movement 
of  the  plate  and  in  locating  its  final  position  whereas,  with  the 
improved  notch,  one  side  does  the  turning  while  the  other  side 
does  the  locating.  The  author  calls  this  action  the  division 
of  functions  and  it  appears  in  various  forms  in  connection  with 
precision  work  and  always  with  improved  durability,  accuracy 
or  other  advantage. 

The  notch  under  discussion  has  another  advantage.  In  the 
truncated  V  notch,  both  sides  are  equally  concerned  with  the 
indexing  and  hence  both  must  be  made  with  equal  accuracy. 
In  the  improved  notch,  since  one  side  only  is  concerned  with 
the  indexing,  that  side  only  need  be  made  with  high  accuracy 
and  hence  the  cost  of  the  work  is  reduced. 

A  still  further  improvement  has  been  made  on  this  construc- 
tion by  the  National  Acme  Manufacturing  Company  through 
an  additional  application  of  the  same  principle.  As  so  far 
shown,  the  division  of  functions  is  between  the  two  sides  of 
the  latch  bolt,  and  there  remains  a  slight  sliding  of  the  index 
side  of  the  bolt  on  the  corresponding  side  of  the  notch  during 
the  small  movement  in  which  the  tightening  of  the  bolt  is 
effected.  In  the  Acme  construction  the  division  is  between 
two  separate  bolts.  The  indexing  bolt  first  enters  its  notch  to 
its  full  depth  and  without  contact  with  the  side  of  the  notch, 
when  the  bolt  which  moves  the  turret  enters  its  notch  and 
moves  the  index  side  of  the  notch  to  contact  with  the  index 
bolt  and  absolutely  without  sliding. 

It  should  be  observed  that  the  importance  of  this  feature 
is  confined  to  working  plates  for  continuous  use,  such  as  those 
by  which  the  turrets  of  turret  lathes  are  fitted.  Some  of  the 
methods  of  precision  indexing  involve  the  use  of  a  master  plate 
which  is  used  only  to  produce  working  plates  by  copying. 
Such  use  of  the  master  plate  is  too  limited  to  introduce  ap- 
preciable wear,  and  the  improved  notch  must  usually  be 
sacrificed  in  master  plates  in  order  to  accommodate  the  proc- 
ess by  which  they  are  produced.  Again,  for  tool  room  work, 
the  use  of  the  plate  is  too  limited  to  introduce  much  wear, 


58 


METHODS  OF  MACHINE  SHOP  WORK 


and  plates  for  such  work  usually  have  round  holes  and  index 
pins. 

Many  methods  of  producing  precision  index  plates  have  been 
used  and,  of  these,  it  is  only  possible  to  show  here  two  which 
are  selected  in  order  to  indicate  the  leading  methods  of  at- 
tack, of  which  other  plans  are,  to  a  large  extent,  variations. 


THE  STEP-BY-STEP  METHOD  OF  ORIGINATING  INDEX  PLATES 

Fig.  41  shows  the  method  used  by  Professor  Rogers  for 
graduting  the  dividing  wheel  of  the  Cornell  University  dividing 
engine  in  which  machine  the  wheel  is  divided  by  lines  for  visual 
reading  and  not  by  notches. 


FIG.  41. — First  method  of  originating  index  plates. 

The  wheel  a  to  be  divided,  which  must  be  of  iron,  has  below 
it  and  in  light  rubbing  contact  with  it,  an  electro  magnet  b 
fitted  with  a  switch  c  by  which  it  may  be  energized  and  de- 
energized.  Swinging  about  the  center  of  the  wheel  is  an  arm 
d  carrying  a  second  electro  magnet  e  which  is  also  provided 
with  a  switch  /.  The  swinging  arm  d  may  be  swung  between 


PRECISION  WORK  AND  WORKMANSHIP  59 

two  stops  g,  //,  of  which  the  latter  is  minutely  adjustable.  At 
i  is  a  fixed  point  carrying  the  stationary  zero  for  reading  the 
graduations. 

By  energizing  e,  swinging  arm  d  to  stop  h,  then  energizing 
b  and  deenergizing  e,  returning  arm  d  to  stop  g  and  then  re- 
peating the  process,  it  is  clear  that  the  wheel  may  be  rotated 
step  by  step,  the  action  being  that  of  a  ratchet  and  pawl  with 
infinitely  fine  teeth.  It  is,  moreover,  clear,  that  by  repeated 
trials,  an  adjustment  of  h  may  finally  be  obtained  such  that 
after  the  required  number  of  movements  the  wheel  a  has  made 
an  exact  revolution.  When  this  adjustment  has  been  found  it 
is  only  necessary  to  repeat  the  step  by  step  movement,  and  make 
a  graduation  mark  on  the  wheel  at  the  completion  of  each  step 
in  order  to  obtain  a  correctly  divided  wheel.  If  desired,  and 
this  was  done  in  the  case  of  the  Cornell  dividing  engine,  addi- 
tional precision  may  be  obtained  by  continuing  the  step  by  step 
movement  during  the  initial  adjustment  until  the  wheel  has 
made  several  revolutions — this  process  multiplying  the  residual 
error  which  might  not  be  apparent  at  the  completion  of  a 
single  revolution.  Moreover,  by  reading  the  lines  through 
a  microscope,  any  conceivable  degree  of  accuracy  may  be 
reached. 

This  method  has  been  a  favorite  one  and  has  many  variations, 
especially  in  the  replacing  of  the  magnetic  action  by  mechanical 
gripping  devices.  It  is  known  as  the  step  by  step  method,  the 
appropriateness  of  which  is  apparent. 

THE  DUPLICATION  METHOD  OF  ORIGINATING  INDEX  PLATES 

For  the  division  of  index  plates  which  are  to  be  used  by  the 
application  of  stationary  latch  pins  or  bolts  and  not  by  visual 
reading,  the  method  which  was  developed  in  connection  with 
the  Thome  typesetting-machine,  and  which  is  now  used  in  the 
production  of  the  Unitype,  appeals  to  the  author  as  the  most 
satisfactory  of  all,  since,  in  addition  to  the  highest  degree  of 
precision  it  is,  compared  with  most  other  methods,  of  moderate 
cost.  In  principle  it  is  as  follows: 

In  Fig.  42  a  disc,  which  is  to  become  the  index  plate,  has  a 


60 


METHODS  OF  MACHINE  SHOP  WORK 


ledge  a  turned  upon  it.  A  number  of  smaller  discs  b,  equal  in 
number  to  the  divisions  required  are  made — such  discs  being 
about  the  easiest  of  all  things  to  make  of  a  high  degree  of 
accuracy  and  uniformity.  The  diameters  of  the  ledge  a  and  of 
the  discs  b  are  so  calculated  that,  when  the  discs  are  placed  in 
position  on  the  ledge,  they  will  make  contact  with  the  ledge 
and  with  each  other.  It  only  remains  to  secure  them  in  posi- 
tion by  means  of  the  cap  screws  shown,  when  the  structure 
forms  a  correct  index  plate. 


FIG.  42. — Second  method  of  originating  index  plates. 

ORIGINATING  INDEX  WORM  WHEELS 

In  a  very  common  form  of  gear  cutting  machine  the  indexing 
of  the  gear  teeth  is  dependent  upon  a  large  worm  wheel  mounted 
upon  the  shaft  which  carries  the  blank  operated  upon,  and 
there  is  the  same  necessity  for  precision  workmanship  in  this 
worm  wheel  as  in  index  plates.  A  method  of  constructing  these 
worm  wheels  has  come  down  to  us  from  early  times  and  is  still 
in  use. 

The  work  is  done  upon  a  hobbing  machine  which  it  is  first 
necessary  to  describe.  Such  a  machine,  by  the  Newton  Machine 


PRECISION  WORK  AND  WORKMANSHIP 


61 


Tool  Works,  is  shown  in  Fig.  43,  a  worm  wheel  in  process  of 
being  cut  appearing  mounted  on  its  spindle  while  behind  and 


FIG.  43. — Worm  wheel  bobbing  machine. 


FIG.  44. — A  hob. 

concealed  by  it  and  mounted  on  the  cutter  spindle  is  a  hob 
which  does  the  work.     A  hob  is  shown  in  Fig.  44.     It  is  a  cross 


62 


METHODS  OF  MACHINE  SHOP  WORK 


between  a  milling  cutter  and  a  tap  or,  otherwise  described,  it 
is  a  worm  suitably  gashed  and  relieved  to  make  it  a  cutting 
tool.  The  worm  wheel  and  hob  spindles  are  connected  by 
gearing,  partly  shown  in  Fig.  43,  by  which  the  wheel  blank  is 
made  to  turn  past  the  hob  as  the  latter  revolves,  precisely  as 
though  the  hob  were  a  worm  and  the  blank  a  finished  worm 
wheel.  With  the  parts  in  motion  as  described,  the  blank  is 
slowly  fed  toward  the  hob  which  thus  cuts  the  teeth. 


FIG.  45. — Construction  of  precision  worm  wheels. 

When  a  precision  worm  wheel  is  to  be  originated  the  blank 
for  it  is  made  in  the  manner  shown  in  Fig.  45,  the  rim  being  in 
halves  as  shown  and  the  two  halves  being  secured  together  by 
taper  pins  of  which  there  are  at  least  four  and  sometimes  more. 
The  holes  for  these  pins  are  so  accurately  spaced  that  the  rings 
may  be  turned  upon  each  other  and  the  pins  be  seated  in  the 
holes  in  any  position.  The  spacing  of  these  holes  so  that  they 


FIG.  46. — Appearance  of  worm  wheel  teeth  when  halves  are  reversed. 

will  meet  this  requirement  is  itself  a  precision  job  of  which, 
however,  details  are  not  here  given. 

The  worm  wheel  blank  being  placed  in  position  on  the  hob- 
bing  machine  the  teeth  are  cut,  following  which  the  rings  are 
separated,  turned  half  way  around  relative  to  each  other  when 
the  pins  are  again  seated  in  their  holes.  In  this  new  position 
of  the  parts  the  two  halves  of  the  teeth  will  be  found  not  to 


PRECISION  WORK  AND  WORKMANSHIP 


63 


match  perfectly,  most  of  them  being  offset,  as  shown  in  Fig.  46, 
though  by  varying  amounts.  The  wheel  is  then  replaced  in 
the  hobbing  machine,  the  gearing  which  connects  the  hob 
and  wheel  is  disconnected  and  the  hobbing  is  repeated,  the  teeth 
of  the  wheel  finding  their  own  places  in  the  hob.  Consulting 


TIG.  47. — Freeland  geer  cutting  machine  known  to  have  been  in  use  in  1857. 

Fig.  46,  it  is  obvious  that  substantially  the  same  amount  of 
metal  will  be  removed  from  one  side  of  one  half  and  the  oihc- 
side  of  the  other  half  of  each  tooth,  the  result  being  a  great 
improvement  in  the  work.  When  the  offsets  of  the  teeth  have 
been  removed  the  parts  are  again  separated,  turned  one-quarter 


64  METHODS  OF  MACHINE  SHOP  WORK 

of  the  way  around  and  the  nobbing  process  is  repeated — again 
with  improvement.  This  process  is  continued  until  the  teeth  of 
the  two  halves  match  in  all  positions,  when  the  worm  wheel  is 
correct. 

A  striking  illustration  of  the  high  ideals  that  prevailed  in  some 
quarters  in  former  times  is  shown  in  Fig.  47,  which  illustrates 
a  small  gear-cutting  machine  made  by  Mr.  Freeland  and  known 
to  have  been  in  use  by  him  in  1857,  the  illustration  being 
from  a  photograph  made  when  the  Freeland  Tool  Works  were 
dismantled  in  1896.  The  worm  wheel  is  clearly  shown  below 
the  bed  as  are  the  bolts  by  which  its  two  halves  are  secured 
together.  It  was  unquestionably  made  by  this  rehobbing 
process.  Another  refinement  which  would  not  be  looked  for 
in  a  machine  of  that  date  is  found  in  the  adjusting  screw  and 
hand  wheel  at  the  rear  for  adjusting  the  cutter  to  depth,  which 
is  fitted  with  a  graduated  circle  reading  to  thousandths  of  an  inch. 
This  machine  is  one  of  several  illustrations  of  advanced  designs 
by  early  constructors  which  these  pages  contain.  Compare 
this  illustration  with  Fig.  256,  which  shows  a  modern  machine 
which,  except  for  its  increased  size  and  the  changed  location 
of  the  crank  and  gearing  by  which  the  worm  wheel  is  turned, 
scarcely  differs  from  the  Freeland  machine  and,  to  carry  the 
parallel  still  further,  the  worm  wheel  of  the  modern  machine 
was  made  by  the  same  process.1  Mr.  Freeland  is  not,  how- 
ever, to  be  regarded  as  a  mere  copyist.  In  planing  machines,  for 
instance,  he  introduced  improvements  for  the  use  of  which  others 
paid  him  royalties  during  the  life  of  his  patents.  Other  con- 
structors, including  Sir  W.  G.  Armstrong  Whitworth  and  Com- 
pany, continue  to  use  the  same  general  construction,  than  which, 
for  a  non-automatic  machine,  there  is  nothing  better. 

1  The  Freeland  machine  is  so  very  Whitworthesque  in  its  outlines,  and  Mr. 
Freeland  was  such  a  disciple  of  Whitworth,  that  it  is  more  than  probable  that 
the  design  of  this  machine  came  from  the  Whitworth  works. 


CHAPTER  III 

MEASURES  OF  LENGTH 

The  metric  fallacy — The  origin  of  measures  of  length — Relative 
accuracy  of  line  and  end  measures— Relation  of  accuracy  of  measurement 
to  character  of  surfaces — Source  of  error  in  shop  use  of  line  measures- 
Methods  of  avoiding  this  source  of  error — Early  history  of  measuring 
machines — The  line  measure  as  a  standard — Characteristic  features  of 
modern  measuring  machines — The  micrometer  caliper — Precision  lathes 
for  cutting  precision  screws. 

THE  METRIC  FALLACY 

A  discussion  of  measures  of  length  for  the  machine  shop  natu- 
rally includes  some  consideration  of  the  metric  system. 

The  old  claims  for  the  almost  universal  use  of  this  system  have 
been  turned  to  ridicule.  The  imposing  list  of  forty-four 
countries  in  which  the  system  was  gratutiously  assumed  by  its 
advocates  to  be  "in  habitual  and  customary  use"  have  dwindled 
under  searching  examination  to  a  few  in  Western  Europe  where 
the  use  of  the  system  is  compulsory.  The  other  countries  of 
the  list  have  passed  laws  of  two  general  kinds,  one  of  which 
merely  legalizes  the  system — that  is,  makes  its  use  permissive — 
while  the  other  adopts  it  as  an  official  government  system  but 
without  compulsion  on  the  people.  Neither  has  resulted  in 
any  appreciable  adoption  of  the  system  in  trade  and  commerce, 
while  in  no  country  whatever  have  compulsory  laws  of  the  most 
sumptuary  character  succeeded  in  eradicating  old  units. 

NON-DECIMAL  UNITS  PREFERRED  BY  THE  PEOPLE  EVERYWHERE 

The  people  everywhere  show  substantially  unanimous  pref- 
erence for  their  old  non-decimal  units,  even  after,  in  some  coun- 
tries, several  generations  of  use  of  the  new  and  in  spite  of  the 
imposition  of  legal  penalties.  This  preference  can  be  explained 
in  two  ways  and  in  two  only :  Either  the  old  units  are  preferred 
because  they  have  been  found  better  for  their  purpose  than  the 
5  65 


66  METHODS  OF  MACHINE  SHOP  WORK 

new,  after  long  trial  of  the  latter,  or  the  change  from  the  old  to 
the  new  system  is  so  difficult  that  even  compulsory  laws  are 
not  able  to  bring  it  about.  It  is  for  the  metric  party  to  choose 
between  the  horns  of  this  dilemma,  either  of  which  is  fatal  to 
their  case. 

The  broad  fact  stands  out  that  in  no  country  whatever — 
France  included — have  the  people  adopted  the  system  in  trade 
and  commerce  because  of  its  supposed  advantages.  Where- 
ever  and  to  whatever  extent  it  is  used  in  trade  and  commerce, 
its  use  is  due  to  compulsion.  Were  the  advantages  claimed  for 
it  real,  compulsion  would  long  ago  have  become  unnecessary. 
The  adoption  of  improvements  is  always  because  of  their  merits 
and  were  the  metric  system  an  improvement  it  would  be  adopted 
for  that  reason. 

Dissipated  also  are  the  old  claims  for  the  ease  of  adoption 
of  the  system.  In  view  of  the  continued  use  of  old  units  in 
France  after  more  than  a  century  of  effort  to  suppress  them,  it  is 
only  through  crass  ignorance  or  worse  that  the  adoption  of  the 
system  can  longer  be  represented  as  an  easy  matter. 

The  foundation  feature  of  the  system  is  that  it  is  a  decimal 
system,  the  ratio  of  each  unit  to  the  one  above  it  being  ex- 
pressed by  the  number  ten.  This  feature  was  introduced  in 
order  to  bring  the  system  into  harmony  with  our  system  of 
arithmetical  notation,  and  to  bring  about  a  supposed  con- 
venience in  calculations  which  forms  the  chief  argument  for  the 
claimed  superiority  of  the  system,  although  it  is  purchased 
at  the  expense  of  all  other  qualities  and  properties  which  a 
system  of  weights  and  measures  should  have.  The  argument 
for  simplicity  of  calculations  has  been  exaggerated  beyond  all 
reason,  while  the  disadvantages  which  accompany  the  decimal 
feature  have  bteu  ignored. 

To  bolster  up  the  claim  for  convenience  in  calculations  the 
metric  party  give  hypothetical  problems  to  solve.  They  as- 
sume, for  example,  a  distance  of  so  many  miles,  furlongs,  rods, 
yards,  feet  and  inches,  show  the  number  of  figures  required  to 
reduce  this  expression  to  inches  and  then  give  a  corresponding 
problem  in  which  distances  are  expressed  in  kilometers,  hekto- 
meters,  dekameters,  meters,  decimeters,  centimeters  and  milli- 


MEASURES  OF  LENGTH  67 

meters  and  show  that  the  expression  can  be  reduced  to  milli- 
meters by  the  simple  process  of  properly  locating  the  decimal 
point.  Similarly  they  show  the  amount  of  work  involved  in 
reducing  an  immense  number  of  inches  to  miles,  furlongs,  rods, 
etc.,  and,  alongside,  they  place  an  exhibit  showing  that  milli- 
meters may  be  rednced  to  kilometers  etc.,  hektometers,  etc.,  by 
merely  changing  the  decimal  point. 

THE  USE  OF  SINGLE  UNITS  NULLIFIES  THE  CLAIMS  MADE 

The  trouble  with  these  problems  is  that  they  are  purely 
hypothetical.  No  one  has  them  to  do — no  reader  of  these  pages 
has  occasion  to  solve  problems  that  are  so  much  as  comparable 
with  those  on  which  the  metric  case  is  based.  With  the 
exception  of  feet  and  inches  which  are  used  in  combination, 
although  the  tendency  is  against  the  practice,  quantities  are 
commonly  expressed  in  single  units.1  Thus  the  flow  of  aque- 
ducts and  the  capacity  of  pumping  engines  and  of  city  reser- 
voirs are  given  in  gallons  and  the  strength  of  materials  in  pounds 
per  square  inch.  Similarly,  when  we  buy  small  quantities  of 
things  at  the  drug  store  we  do  it  by  the  ounce  and  its  fractions, 
while,  if  we  buy  larger  quantities  at  the  grocery,  we  do  it  by  the 
pound  and  its  fractions — pounds  and  ounces  being,  practically, 
never  mixed.  Again,  we  buy  milk  by  the  quart,  gasolene  by  the 
gallon,  grain  by  the  bushel,  and  cement  by  the  barrel,  but  no 
American  reader  of  these  pages  ever  sees  these  units  used  con- 
jointly. The  civil  engineer  uses  the  mile  as  his  long  and  the 
foot  as  his  short  unit  of  length — these  units  being  divided  deci- 
mally for  purposes  of  measurement  and  calculation — but  he 
never  uses  the  two  in  combination.  His  unit  of  excavation  is 
the  cubic  yard,  but,  like  the  others,  it  stands  alone.  Reduction, 
ascending  or  descending,  among  these  units  is  among  the  rarest 
of  problems  and  the  ratios  between  them  are  about  the  least 
important  things  that  ever  produced  a  heated  discussion. 

Not  only  is  this  the  method  by  which  these  units  are  used 
but  it  is  the  manner  in  which  they  were  intended  to  be  used. 
Units  of  different  sizes,  English  and  metric  alike,  are  provided 

1  This  practice,  while  almost  universal  in  the  United  States,  is  not  so  common 
in  Great  Britain. 


68  METHODS  OF  MACHINE  SHOP  WORK 

in  order  that  those  suitable  for  various  purposes  may  be 
available.  The  quart  being  suitable  for  the  amount  of  milk 
commonly  purchased,  the  quart  is  used  for  that  purpose, 
while  the  gallon  being  suitable  for  the  amount  of  gasolene 
commonly  purchased,  the  gallon  is  used  for  that  purpose. 
For  the  same  reason  the  ounce  is  used  for  the  purchase  of 
drugs,  the  pound  for  groceries  and  the  ton  for  coal.  The  use 
of  a  mixture  of  units  for  the  same  purpose  is  uncalled  for  and 
unnatural  and  its  appearance  in  the  problems  referred  to  is 
simply  a  case  of  manufacturing  evidence  to  suit  the  case 
which  it  is  desired  to  prove. 

Using  units  in  this  manner,  the  importance  of  the  ratios 
between  them  sinks  into  insignificance.  For  purposes  of 
calculation  they  may  be  divided  decimally,1  as  they  usually 
are,  when  they  fall  into  perfect  harmony  with  decimal  arithmetic. 
Used  in  this  way,  no  discoverable  difference  in  the  time  required 
for  calculations  in  the  English  and  the  metric  systems  has  ever 
been  shown  because  none  exists.  The  engineer  calculates 
stresses  or  pressures  in  pounds  per  square  inch  with  absolutely 
the  same  simplicity  of  calculation  that  he  does  in  kilograms 
per  square  centimeter.  So,  also,  the  dimensions  of  structural 
members  are  calculated  in  inches  with  the  same  degree  of 
simplicity  as  in  millimeters  and  hydraulic  calculations  in 
gallons  are  as  simple  as  in  liters. 

TEN  A  BAD  DIVISOR 

From  whatever  other  constructor's  standpoint  the  matter 
is  viewed,  the  metric  system  is  at  a  disadvantage,  and  this 
because  its  base,  ten,  is  awkward  and  inflexible.  It  is  well 
known  to  all  who  have  given  the  subject  attention,  that  one 
of  the  misfortunes  under  which  the  human  race  suffers  is  the 

1  The  metric  party  labors  under  a  strange  hallucination  that  they  possess  a 
monopoly  of  decimal  arithmetic  and  they  hail  every  use  of  decimals  as  a  conces- 
sion to  their  claims.  Decimal  fractions  are,  of  course,  centuries  older  than  the 
metric  system,  the  fathers  of  which  system  adopted  but  did  not  originate  them. 
With  the  English  system  they  are  used  when  convenient  and  dropped  when  in- 
convenient. With  the  metric  system,  on  the  contrary,  they  must  be  used 
whether  convenient  or  not. 


MEASURES  OF  LENGTH  69 

fact  that  our  system  of  arithmetic  is  based  on  ten.  It  has  been 
truly  said  that  of  all  even  numbers  below  twenty,  ten  is  the 
worst  possible  choice  for  this  purpose  with  the  single  exception 
of  fourteen,  and  if  ten  is  a  bad  base  for  a  system  of  arithmetic, 
much  more  is  it  a  bad  one  for  a  system  of  weights  and  measures. 
In  the  constructive  arts,  the  badness  of  the  divisor  ten  shows 
itself  chiefly  in  its  inflexibility  as  regards  the  sizes  which  are 
possible  under  it.  It  is  a  basic  feature  of  all  manufacturing 
that  of  the  many  sizes  which  are  possible  but  few  shall  be 
used.  Thus  between  one  and  two  inches  we  have  but  eight 
sizes  of  standard  screw  threads,  while  of  shafting  we  have  but 
four  and  of  pipe  but  three.  For  constructive  purposes  the 
basic  requirement  of  a  system  of  measurement  is  that  the  choice 
of  these  sizes  shall  be  flexible  and  herein  division  by  successive 
halving  is  infinitely  superior  to  division  by  ten. 

THE  MANUFACTURER'S  CASE  AGAINST  THE  SYSTEM 

The  chief  objection  to  the  adoption  of  the  system  is,  however, 
that  it  involves  a  complete  change  in  the  established  system  of 
sizes  used  in  manufacturing — a  change  so  difficult  that  it  has 
not  been  completed  in  any  so-called  metric  country. 

Fig.  48  shows  an  English  and  a  metric  scale  in  contact. 
The  base  units  of  the  two  systems  being  incommensurate,  their 
divisions  cannot  agree  and  the  two  sets  of  lines  seem  to  fairly 


1,1,1,1,1,1,1 


in 


III  I  II  I  III  II  IIII  Illl  III!  Illl  I 


5 6 7       6 9 1 


FIG.  48. — English  and  metric  scales. 

play  a  game  of  hide  and  seek  in  their  efforts  to  elude  one  another. 
The  lines  upon  the  English  scale  give  the  dimensions  to  which 
things  have  always  been  made  in  English-speaking  countries 
and,  reduced  to  its  lowest  terms,  the  proposition  is  that  these 
sizes  shall  be  abandoned  and  those  shown  on  the  metric  scale 
substituted  for  them,  and,  not  only  are  the  English  sizes  to  be 
abandoned,  but  the  established  mechanical  standards  based 
upon  them  as  well.  ^-  f 


70  METHODS  OF  MACHINE  SHOP  WORK 

Consider  the  couplings  with  which  the  air  brake  hose  ends  of 
railroad  cars  are  coupled  together.  These  couplings  have  been 
standardized  by  the  Westinghouse  Air  Brake  Company,  and, 
because  of  this  and  standardized  draft  couplers,  railroad  cars 
of  all  American  lines  interchange  as  a  matter  of  course.  The 
attempt  to  change  them  would  lead  to  confusion  worse  con- 
founded, and,  the  new  couplings  being  no  better  than  the  old,  it 
would  accomplish  no  useful  purpose.  It  is  not  a  matter  of 
willingness  to  change,  nor  of  getting  people  to  think  in  the  new 
units,  nor  of  the  length  of  life  of  individual  couplings,  nor  of  the 
tools  that  make  them.  The  obstacle  to  the  change  is  physical; 
the  simple  necessity  for  continuity  between  old  and  new  coup- 
lings requires  the  continuance  of  the  present  standard. 

This  example  is  selected  not  because  the  difficulty  of  the 
change  here  is  greater  than  elsewhere,  but  because  it  is  so  plain 
as  to  be  obvious  after  the  slightest  reflection.1  "  Measures  of 
length  are  tied  irrevocably  to  the  past."  The  overwhelming 
difficulties  of  these  changes  growing  out  of  the  simple  necessity 
for  continuity  of  sizes  between  old  and  new  constructions 
pervade  every  application  of  measures  of  length  in  the  con- 
structive arts,  takes  the  subject  from  the  realm  of  choice  and 
makes  the  change  in  such  applications  impossible. 

THE  USE  OF  METRIC  EQU1VALEKTS  OF  EXISTING  SIZES 
IMPOSSIBLE 

Until  recent  years  the  metric  party  have  ignored  this  diffi- 
culty.2 Repeated  insistence  upon  it  as  the  prime  reason  for 
the  objections  of  manufacturers  to  the  change  has  now  com- 
pelled the  metricites  to  take  notice  of  it  and  they  suggest, 
as  a  means  of  getting  around  it,  the  continued  use  of  existing 
sizes  expressed  in  millimeters  and  fractions  thereof,  a  sugges- 

1  Other  examples  are  screw  threads,  pipe  and  pipe  fittings,  shafting  and  pulleys, 
diametral  pitch  gears,  rolled  shapes  and  the  numerous  standards  of  the  Railway 
Master  Mechanic's  Association. 

2  Because  that  party  is  composed  chiefly  of  scientific  men.     The  use  of  a  defined 
set  of  sizes,  which  is  the  characteristic  feature  of  manufacture,  has  no  place  in 
the  scientific  use  of  weight  and  measure,  which  consists  in  measuring  things  as 
they  happen  to  be.     Having  no  knowledge  of  manufacturing,  scientific  men 
naturally  ignore  it,  and,  by  the  same  token,  their  opinions  regarding  the  use  of 
the  system  in  manufacture  have  no  value. 


MEASURES  OF  LENGTH  71 

tion  that  is  too  amateurish  to  merit  discussion  were  it  not  offered 
seriously  and  repeatedly. 

In  this  they  show  a  hopeless  incapacity  to  understand  the 
difference  between  measuring  and  making.  The  element  of 
choice  of  dimensions  is  absent  from  the  process  of  measuring. 
Things  are  measured  as  they  happen  to  be,  whereas  they  are 
made  of  sizes  which  are  deliberately  chosen,  and  the  chosen  sizes 
are  those  shown  by  the  lines  on  the  measuring  scales  used. 
Since  the  sets  of  sizes  which  characterize  the  two  systems  do 
not  agree,  it  follows  that  if  the  sizes  shown  by  the  lines  of  one 
scale  are  to  be  expressed  in  units  of  the  other,  draftsmen  and 
mechanics  will  be  required  to  use  a  set  of  sizes  which  are  not 
given  by  the  lines  on  the  scales  from  which  they  are  taken. 
That  is  to  say,  instead  of  taking  from  the  scales  the  sizes  shown 
by  their  lines,  intermediate  sizes  are  to  be  taken  by  estimation. 
Worse  yet,  from  the  draftsman's  standpoint,  the  set  of  sizes 
which,  as  expressed  on  English  scales,  fairly  memorize  them- 
selves, become,  when  expressed  in  metric  units,  a  series  of  such 
character  that  the  memorizing  of  it  is  impossible,  and  yet  this 
must  be  done  if  this  specious  scheme  is  to  be  carried  out. 

The  impossibility  of  memorizing  this  series  of  equivalents 
will  be  apparent  from  a  glance  at  the  accompanying  table. 

METRIC  EQUIVALENTS  OF  ENGLISH  SIZES 

ins.                  mm.  ins.  mm. 

i                      25.4  2  50.8 

if                   38.57  ~l  53-97 

ii                   31-75  2\  57.15 

if                   34-92  2|  60.32 

I*  38.1  2i  63-5 

l|  41.27  2|  66.67 

if  44.45  2|  69.85 

l|  47.62  2|  73.02 

3  76.2 

The  combinations  of  figures  do  not  repeat  themselves, 
each  added  inch  adding  a  new  set  of  combinations,  which  is  to 
say  that  the  table  has  no  end.  The  metric  party  will  tell  us 
that  this  table  is  to  be  used  "  during  the  transition  period 
only, "  but  the  transition  period  is  not  yet  past  in  France,  and  it 


72  METHODS  OF  MACHINE  SHOP  WORK 

will  not  be  past  in  the  United  States  until  all  existing  mechanical 
standards  are  abandoned. 

Is  it  reasonable  to  suppose  that  eight  threads  per  inch  will 
ever  be  translated  into  eight  threads  per  twenty-five  and  four- 
tenths  millimeters,  or  that  six  diametral  pitch  will  be  thought 
of  as  meaning  six  teeth  per  twenty-five  and  four-tenths 
millimeters  diameter?  Will  six-inch  shafting  ever  be  thought 
of  as  one  hundred  fifty- two  and  four-tenths-millimeter  shafting  or 
twelve  inch  I-beams  as  three  hundred  four  and  eight-tenths- 
millimeter  beams? 

Let  the  reader  turn  to  the  metric  scale  of  Fig.  49  and  by  it 
attempt  to  lay  down,  as  a  draftsman  would  have  to  do,  a  few 
such  sizes  as  yV>  Jf ,  and  3!  inches.  Explanation  is  unneces- 
sary. If  the  reader  will  but  try  it  the  simple  childishness  of 


FIG.  49. — Metric  scale. 

the  scheme  will  be  apparent.1  And  yet  it  is  to  this  pitiful 
thing  that  the  metric  case  has  been  reduced.2  The  preserva- 
tion of  mechanical  standards  is  admitted  to  be  a  necessity. 
If  they  are  to  be  continued  and  the  metric  system  is  to  be  used 
in  connection  with  them,  this  plan  must  be  made  to  work, 
and  made  to  work  it  cannot  be. 

Cannot  the  metric  party  see  that  if  the  plan  were  workable 
it  would  have  been  adopted  years  ago  in  metric  countries? 
Such  countries  would  not,  as  they  all,  in  fact,  do,  measure  screw 
threads,  pipe  and  lumber  in  inches,  were  it  feasible  to  thus 
express  the  sizes  of  one  system  in  the  units  of  another. 

THE  PERSISTENCE  OF  OLD  UNITS  INVERTS  ALL  ARGUMENTS  FOR 

THE  SYSTEM 

Dismissing  this  scheme,  nothing  is  more  certain  than  that 
existing  mechanical  standards  will  not  be  changed.  The  only 

1  The  object  of  the  plan  is  to  retire  the  inch  from  men's  thoughts  as  well  as 
from  the  drafting  board.     The  use  of  a  table  of  equivalents  is  therefore  inadmis- 
sible. 

2  See  the  Value  World  for  March,  1913,  where  the  plan  is  urged  in  all  its  bald 
absurdity. 


MEASURES  OF  LENGTH  73 

effect  of  the  adoption  of  the  system  would  be  to  superimpose  it 
on  the  existing  system.  In  some  applications  the  change  is 
not  difficult  and  in  such  applications  it  would  be  made,  while 
in  the  applications  that  have  been  discussed  the  old  units  will 
be  continued.  The  net  result  would  be,  as  it  uniformly  has 
been  elsewhere,  the  conjoint  use  of  both  systems.  The  in- 
commensurate ratios  between  the  units  of  the  two  systems  are 
far  worse  than  any  existing  ratios.  In  other  words,  at  the 
very  point  at  which  the  system  is  urged  in  order  to  make  matters 
better  than  now,  it  would,  in  fact,  make  them  far  worse. 
The  ratio 

3  feet  make  i  yard 

is  held  up  as  an  example  of  all  that  is  bad  and  as  the  cause 
of  complexity  in  calculations,  but  the  ratio 

3.28083  feet  make  i  meter 

is  accepted  without  a  murmur.  Moreover,  while,  as  has  been 
pointed  out,  the  ratios  between  English  units  seldom  enter 
calculations  because  different  English  units  are  used  for  dif- 
ferent purposes,  the  ratios  between  English  and  metric  units 
frequently  enter  calculations  because  corresponding  units  of 
the  two  systems  are  used  for  the  same  purposes — the  uses  of  the 
inch  and  millimeter  and  of  the  pound  and  kilogram  being 
identical.  It  is  for  this  reason  that  every  engineer's  reference 
book  contains  extended  tables  to  facilitate  conversion  calcu- 
lations between  the  two  systems. 

All  arguments  for  the  adoption  of  the  system  rest  upon  the 
tacit  assumption  that  the  old  units  are  to  disappear.  If  the 
old  units  are  to  persist,  every  argument  for  the  system  inverts 
itself  and  becomes  an  argument  against  it.  Thus,  instead  of 
uniformity  we  would  have  diversity  of  units,  instead  of  simpler 
more  complex  ratios,  instead  of  simplified  more  complex 
calculations,  and  so  on  to  the  end.  In  the  final  analysis,  the 
effect  of  this  conjoint  use  of  old  and  new  units  is  the  chief 
thing  to  be  considered.  It  is  found  in  every  metric  country — 
France  included — and  it  not  only  nullifies  but  reverses  every 
metric  argument. 


74  METHODS  OF  MACHINE  SHOP  WORK 

THE  METER  SHOULD  HAVE  BEEN  ABANDONED  WHEN  ITS  ERROR 
WAS  DISCOVERED 

It  is  well  known  and  universally  acknowledged  that  the 
attempt  to  derive  the  meter  from  a  measurement  of  an  arc  of  a 
meridian  of  the  earth's  surface  was  a  failure.  The  actual  base 
meter  is  the  distance  between  two  lines  ruled  on  a  standard 
bar  of  which  all  other  meters  are,  directly  or  indirectly,  copies. 
With  the  error  of  the  survey  proven,  the  meter  had  no  longer  an 
excuse  for  existence.  It  then  became  an  arbitrary  unit  like 
the  yard  and  in  no  manner  nor  degree  better  than  the  yard, 
while  the  effect  of  its  continuance  was  the  introduction  of  an- 
other base  unit  of  which  the  world  already  had  too  many.  The 
discovery  of  the  error  was  made  before  the  adoption  of  the  meter 
had  made  much  progress  and  when  it  could  easily  have  been 
changed,  and,  in  view  of  the  established  position  of  the  yard, 
the  surveyed  value  should  have  been  abandoned  as  the  result 
of  a  well  meant  but  abortive  attempt  to  establish  a  natural 
unit. 

After  the  error  had  been  discovered  and  the  significance  of  the 
surveyed  value  destroyed,  Sir  Joseph  Whitworth,  realizing 
the  consequences  of  incommensurate  ratios,  urged  that  the 
length  of  the  meter  be  changed  to  forty  inches  (an  increase  of 
about  five-eighths  of  an  inch).  This  small  change  would  have 
made  the  decimeter  exactly  equal  to  four  inches  and  twenty- 
five  millimeters  exactly  equal  to  one  inch,  the  incommensurate 
ratios  disappearing.  The  suggestion  fell  upon  deaf  ears.  The 
system  had  already  become,  what  it  now  is,  a  sort  of  religion. 
The  meter  had  taken  on  a  sacrosanct  character  and  a  change  in 
its  value  was  looked  upon  as  sacrilege.  For  no  better  reason 
than  this — the  simple  worship  of  a  fetich — the  most  sane  and 
useful  suggestion  ever  made  in  connection  with  the  system,  and 
one  from  the  man  of  all  men  best  able  to  speak  with  authority 
and  best  deserving  a  hearing,  came  to  nothing.  The  incom- 
mensurate ratios  were  fastened  upon  the  world,  and  the  irony 
of  it  is  that  this  was  done  in  the  name  of  simplified  ratios. 

The  most  ardent  advocate  of  the  system,  as  a  system,  if  he 
is  not  purblind,  cannot  fail  to  see  that  the  introduction  of  a 
new  incommensurate  base  unit,  having  in  itself  no  element  of 


MEASURES  OF  LENGTH  75 

superiority,  had  no  justification  and  was  certain  to  lead  to  con- 
fusion and  complexity  instead  of  clarity  and  simplicity.  Those 
who  did  it  in  the  interest  of  a  needless  revolution  have  their 
reward,  for  they  but  added  another  obstacle  to  the  adoption 
of  their  system. 

The  anti-metric  case  is,  however,  far  too  large  a  subject  to  be 
adequately  treated  here.  For  additional  voluminous  informa- 
tion the  reader  is  referred  to  The  Metric  Fallacy  by  the  author 
and  The  Metric  Failure  in  the  Textile  Industry  by  S.  S.  Dale, 
to  contributions  by  the  author  and  others  to  the  Transactions 
of  the  American  Society  of  Mechanical  Engineers,  Vols.  24  and 
28,  and  especially  to  the  official  confession  of  the  French 
Minister  of  Commerce,  Industry  and  Labor  regarding  the 
failure  of  compulsion  to  suppress  old  units  in  France,  Trans. 
A.  S.  M.  E.,  Vol.  28,  p.  877. 

THE  ORIGIN  OF  THE  INCH 

The  absolute  uniformity  of  measures  of  length  throughout  the 
English-speaking  world  is  one  of  the  marvels  of  modern  times. 
Gages  may  be  bought  from  various  makers  located  indifferently 
in  the  United  States,  Great  Britain  or  Sweden,  which,  when 
compared,  are  found  to  agree  to  the  last  measure  of  perfection. 
The  beginning  of  this  uniformity  dates  from  Magna  Charta,  one 
of  whose  provisions  reads:  "There  shall  be  one  weight  and  one 
measure  throughout  our  realm,"  and  while,  of  course,  that  sen- 
tence voiced  an  intention  rather  than  an  immediate  realization, 
it  is  a  fact  that  every  step  in  the  attainment  of  accuracy,  except 
the  last  which  came  from  Sweden,  has  been  the  work  of  the  Eng- 
lish-speaking peoples.  Long  after  uniform  measures,  accord- 
ing to  the  standard  of  accuracy  of  their  time,  were  an  estab- 
lished fact  in  England,  the  French  were  in  the  slough  of  de- 
spond with  numerous  local  standards  of  varying  values.  When 
the  confusion  became  intolerable,  instead  of  standardizing 
their  existing  units  or  adopting  those  already  standardized, 
the  French  developed  an  uncalled-for  new  system,  thereby 
increasing  instead  of  reducing  the  existing  confusion  and 
disorder. 


76  METHODS  OF  MACHINE  SHOP  WORK 

The  uniformity  which  exists  among  measuring  instruments 
obtained  from  different  makers  and  different  countries  is  due  to 
the  fact  that  they  have  a  common  origin,  namely  the  standard 
yard  which  is  deposited  in  the  Standards  Department  of  the 
Board  of  Trade  at  London.  It  is  a  line  measure,  the  distance 
between  two  fine  lines  near  its  ends  being,  by  act  of  the  British 
Parliament,  a  yard,1  and  of  this  yard,  suitably  divided  and  mul- 
tiplied, all  measures  of  length  of  the  English  system  are,  directly 
or  indirectly,  copies.  Extraordinary  safeguards  protect  this 
yard  irom  possible  damage.  It  is  preserved  in  a  vault  from 
which  it  is  taken  once  in  ten  years  for  comparison  with  the 
working  standards.  A  copy  of  this  yard  is  preserved  in  Wash- 
ington, of  which  copies  were  made  by  the  Brown  and  Sharp 
Manufacturing  Company  and  the  Pratt  and  Whitney  Company, 
which  copies  are  the  bases  of  all  measuring  instruments  supplied 
by  those  companies,  of  which  independent  comparisons  have 
shown  an  agreement  that  is  perfect. 

THE  COMPARATIVE  ACCURACY  OF  LINE  AND  END  MEASURES 

Some  comparisons  between  line  and  end  measures  have  al- 
ready been  made,  but  it  is  necessary  to  obtain  a  more  exact 
idea  of  their  relative  accuracy.  The  only  deliberate  determina- 
tion of  the  accuracy  of  line  measures  of  which  the  author  has 
knowledge  was  by  F.  J.  Miller,  who  turned  five  plugs  by  the 
making  process,  these  plugs  being  of  different  sizes  in  order  to 
insure  against  the  formation  of  habit  in  the  setting  of  the  cali- 
pers. The  plugs  were  made  as  carefully  as  possible  without 
using  a  magnifying  glass  in  setting  the  calipers  and,  when 
finished,  they  were  measured  with  a  micrometer.  The  result 
was  to  show  a  maximum  variation  from  truth  of  one  and  one- 
half  thousandths  of  an  inch.  Some  of  the  plugs  were  small 
and  others  large,  the  extreme  variation  between  the  smallest 
and  the  largest  being  two  and  one-half  thousandths. 

This  is  undoubtedly  a  smaller  error  than  would  be  obtained 
if  a  greater  number  of  plugs  had  been  made  and  it  is  certainly 
smaller  than  would  be  found,  if  comparisons  were  made  be- 

1  As  has  already  been  shown  the  meter  stands  upon  exactly  the  same  footing. 


MEASURES  OF  LENGTH  77 

tween  the  work  of  different  men.1  It  was  the  recognition 
of  the  inevitable  error  due  to  the  taking  of  sizes  from  graduated 
scales  that  led  Bodmer,  about  1840,  to  design  plug  and  ring 
gages.  Sizes  can  be  taken  from  such  gages  with  calipers  with  a 
far  higher  degree  of  precision  than  from  graduated  scales. 

A  set  of  Whitworth  plugs  and  rings,  now  the  property  of 
The  American  Society  of  Mechanical  Engineers,  which  were 
imported  into  the  United  States  by  Mr.  Freeland  prior  to  1857, 
is  shown  in  Fig.  50.  Although  the  mating  plugs  and  rings 


FIG.  50. — Whitworth  plug  and  ring  gages. 

are  still  good  fits,  showing  absence  of  wear,  the  gages  are  not  of 
an  accuracy  which  would  now  be  considered  sufficient  for  such 
instruments. 

For  many  years  such  gages  supplied  the  only  means  of 
introducing  standard  measurements  of  their  degree  of  accuracy. 
They  are  still  made  and  are  listed  in  the  catalogues  of  gage 
makers,  but  are  going  out  of  use.  Their  present  use  is  chiefly 
as  reference  gages  for  detecting  wear  of  snap  gages,  for  which 
purpose  they  are  unnecessarily  expensive.  For  this  purpose 
the  ring  gages  are  not  really  required  and  the  plugs  have  an 
unnecessary  extent  of  surface  which  adds  seriously  to  their 
cost.  For  this  use  the  Brown  and  Sharpe  reference  discs,2 
shown  in  Fig.  51,  answer  every  purpose  and  are  much  cheaper. 

1  An  investigation  by  the  Engineering  Standard's  Committee  of  Great  Britain 
showed  the  prevailing  tendency  to  be  to  make  plugs  too  small  and  holes  too  large. 
Of  456  plugs  examined  56  per  cent,  were  too  small,  35  per  cent,  too  large  and  9 
per  cent,  correct.     Similarly  of  329  holes  examined  25  per  cent,  were  too  small, 
62  per  cent,  too  large  and  13  per  cent,  correct.     In  both  cases  the  direction  of  the 
largest  error  was  the  same  as  that  of  the  greatest  number  of  errors. 

2  Gages  of  this  form  and  for  this  purpose  were  first  made  by  John  Richards. 


78 


METHODS  OF  MACHINE  SHOP  WORK 


The  degree  of  accuracy  to  be  expected  from  the  use  of  line 
measures  and  calipers  having  been  shown,  so  far  as  it  has  been 
determined,  it  remains  to  show  the  increased  accuracy  of  end 
measures.  Fig.  52  shows  two  Brown  and  Sharpe  plugs  which 


FIG.  51.— Standard  reference  discs. 

differ  in  diameter  by  a  ten  thousandth  of  an  inch  and  between 
them  is  a  snap  gage.  Trying  this  gage  upon  the  plugs,  the  hand 
of  any  one,  no  matter  how  unskilled,  will  detect,  without 


FIG.  52. — Lapped  plugs  and  snap  gage. 

possibility  of  mistake,  the  larger  plug.  We  have  already  seen 
that,  using  line  measures  and  calipers,  uniformity  within  two 
and  one-half  thousandths  cannot  be  expected,  and  we  have 
here  at  once  a  relative  sensitiveness  between  the  two  methods 


MEASURES  OF  LENGTH  79 

and  under  the  most  favorable  circumstances  for  the  line  measure 
of  twenty-five  to  one.  As  has  been  explained,  moreover,  if 
the  results  obtained  by  different  workmen  were  compared,  the 
result  with  line  measures  would  be  still  worse  while,  by  in- 
creasing the  stiffness  of  the  snap  gage,  its  sensitiveness  may  be 
still  further  increased. 

THE  RELATION  OF  ACCURACY  OF  MEASUREMENT  AND  THE 
CHARACTER  OF  THE  SURFACES  MEASURED 

While  it  is  easy  to  speak  freely  of  such  minute  quantities  as 
the  ten  thousandth  of  an  inch,  and  with  proper  grades  of 
workmanship  to  show  their  existence,  a  word  of  caution  is 
necessary.  The  easy  detection  of  this  quantity  in  the  case  of 
the  Brown  and  Sharpe  plugs  is  due  to  the  perfection  of  their 
surfaces.  We  cannot  measure  a  brick  to  the  sixteenth  of  an 
inch  because  the  errors  of  its  surfaces  exceed  that  amount  and. 
precisely  so,  we  cannot  measure  parts  having  surfaces  made 
with  cutting  tools  to  the  ten  thousandth  of  an  inch,  and  for  the 
same  reason.  The  ten  thousandth  of  an  inch  has  no  place  in 
the  measurement  of  parts  made  with  cutting  tools,  its  place 
appearing  only  in  the  highest  quality  of  work  made  by  grind- 
ing or  lapping.  For  cut  surfaces  the  thousandth  of  an  inch  is 
about  as  small  a  measure  as  has  any  practial  application. 

THE  SOURCE  OF  THE  ERRORS  WHEN  USING  LINE  MEASURES 

It  is  now  necessary  to  point  out  the  source  of  the  error  when 
using  line  measures.  These  measures  may  be  of  any  required 
degree  of  accuracy,  and  the  calipers  used  with  them,  while, 
as  explained  below,  not  equal  to  snap  gages,  are  nevertheless 
end  measures  and  fairly  entitled  to  be  called  precision  instru- 
ments. At  the  same  time,  having  two  instruments  which  are 
individually  accurate,  we  find  their  combination  to  be  the 
reverse.  The  errors  arise  in  the  transfer  of  the  sizes  from  the 
scale  to  the  calipers.  The  workman  is  expected  to  accurately 
divide  the  lines  of  the  scale  by  the  caliper  legs  and  this  he  cannot 
do. 

This  line  measure,  however,  which  gives  many  sizes  from  one 
cheap  instrument  and  the  accuracy  of  which  is  not  impaired  by 
wear,  is  too  serviceable  a  thing  to  be  discarded  and  it  is  only 


80  METHODS  OF  MACHINE  SHOP  WORK 

necessary  to  devise  means  by  which  the  transfer  from  the  line 
to  the  end  measure  can  be  made  with  increased  accuracy  to  make 
the  line  measure  an  accurate  as  well  as  a  useful  instrument. 

For  the  doing  of  this  we  have  four  methods,  namely:  the 
vernier,  the  micrometer,1  the  multiplying  lever  and  the 
microscope. 

THE  VERNIER 

Fig.  53  shows  the  most  obvious  application  of  the  first  of  these 
devices  to  the  vernier  caliper  of  the  Brown  and  Sharpe  Manu- 
facturing Company.  The  line  and  end  measures  are  here  com- 
bined in  one  instrument,  with  screw  adjustment  for  accurate 
setting,  the  adjustment  being  much  more  accurate  than  that  of 
the  common  calipers  applied  to  a  graduated  scale,  by  reason  of 
the  fact  that  the  lines  of  the  vernier  may  be  matched  against 
those  of  the  scale  with  far  greater  accuracy  than  can  the  unlike 
ends  of  the  caliper  legs  and  the  lines  of  the  usual  scale.  The 
verniers  of  these  instruments  are  commonly  so  divided  as  to 
read  to  thousandths  of  an  inch — the  error  of  their  adjustment 
being  naturally  somewhat  less  than  this.  With  finer  division 
lines  and  a  microscope  the  adjustment  may  be  made  still  more 
accurately.  Examples  of  such  verniers  and  microscopes  are 
seen  on  surveying  instruments. 

Figs.  54  and  55  show  height  and  depth  gages  respectively. 
One  application  of  the  former  has  already  been  shown  in  Figs.  32- 
35  and  others  follow.  The  depth  gage  finds  large  use  in  die  sink- 
ing and  other  branches  of  tool  making.  In  the  reading  and 
adjustment  all  these  instruments  are  line,  while  in  use  they  are 
end  measures. 

It  has  already  been  pointed  out  that  the  line  measure  is  free 
from  deterioration  due  to  wear  and  this  makes  such  measures  a 
necessity  for  ultimate  standards.  The  official  standards  of  the 
yard  and  of  the  meter  are  line  measures.2  In  such  standards 

1  The  author  includes  the  micrometer  here  because,  so  far  as  the  reading  of  its 
scale  is  concerned,  it  is  a  line  measure,  in  which  particular  it  is  exactly  parallel 
with  the  vernier  and  the  multiplying  lever. 

2  The  ignorance  of  the  fathers  of  the  metric  system  of  fundamental  requirements 
is  shown  by  the  fact  that  the  original  meter — long  since  discarded — was  an  end 
measure.     The  original  standard  yard  has  always  been  a  line  measure. 


MEASURES  OF  LENGTH 


81 


the  lines  are  so  fine  that  they  cannot  be  seen  with  the  naked 
eye.  They  are  read  through  a  microscope  of  which  the  eye 
piece  carries  a  spider  cross  hair.  While  these  lines  are  extremely 
fine,  they  can  be  read  with  an  error  much  less  than  their  width. 


23456789  I  1254  5fe769jl  25456789  I  I  25456789 i 1 254 5678 9 1 


\ 


FIG.  53. — Vernier  caliper. 


FIG.  54. — Vernier  height  gage. 


FIG.  55. — Vernier  depth  gage. 


If  the  cross  hair  of  the  microscope  is  somewhat  narrower  than 
the  line  upon  the  standard  it  may  obviously  be  centralized  over 
it  with  an  error  much  less  than  the  width  of  the  lines.  Mr. 


82  METHODS  OF  MACHINE  SHOP  WORK 

Bond  informs  the  author  that  his  practice  is  to  match  the 
edge  of  the  cross  hair  against  the  edge  of  the  line. 

THE  HISTORY  OF  MEASURING  MACHINES 

To  the  best  of  the  author's  knowledge  the  history  of  the  shop 
micrometer  begins  with  one  made  by  James  Watt,  now  in  the 
South  Kensington  Museum  and  shown  in  Fig.  56. 1 

This  instrument  has,  curiously  enough,  18  threads  per  inch 
while  its  dial  is  divided  into  100  parts,  making  the  nominal 
value  of  its  indications  the  eighteen  hundredth  of  an  inch.2 


FIG.  56. — James  Watt's  micrometer  caliper. 

While  this  instrument  shows  clearly  enough  the  conception 
of  accuracy  and  a  method  of  obtaining  it,  it  is  not  to  be  imagined 
that  its  real  was  equal  to  its  nominal  accuracy.  It  was  not 
possible  in  Watt's  time  to  make  screws  sufficiently  accurate 
for  such  a  purpose  which,  alone,  would  defeat  the  object  of  the 
instrument. 

The  early  history  of  accurate  shop  measurements  has  already 
been  outlined.  As  regards  end  measures,  Sir  Joseph  Whit- 
worth  exhibited  his  millionth  measuring  machine,  which  is  still 
preserved,  in  1851.  While  this  machine  is  chiefly  of  academic 
interest,  its  construction  marked  an  epoch  in  the  history  of 
accuracy  of  size,  precisely  as  Whitworth's  surface  plates  marked 

1  The  original  application  of  the  micrometer  screw  was  to  the  eye  pieces  of 
telescopes.     It  was  thus  applied  in  1648  and  it  was  largely  through  its  assistance 
that  astronomy  became  an  exact  science. 

2  The  small  dial  on  the  front  sid    of  the  instrument  indicates  the  number  of 
whole  turns  of  the  screw. 


MEASURES  OF  LENGTH  83 

an  epoch  in  the  history  of  accuracy  of  form.  It  should  be  said, 
further,  that  the  machine  would  not  now  be  called  a  measuring 
machine.  Its  purpose  was  not  to  determine  the  absolute 
length  of  pieces  but  to  compare  different  pieces  and  determine 
their  differences.  It  would  now  be  called  a  comparator  rather 
than  a  measuring  machine. 

It  is  difficult  to  conceive  the  crudity  of  measuring  instru- 
ments prior  to  the  dates  that  have  been  given.  End  measures 
were  unknown  prior  to  Whitworth's  work,  while  prior  to  the 
scales  of  Brown  and  Darling,  it  is  not  too  much  to  say  that 
the  carpenter's  square  of  to-day  is  a  precision  instrument  in 
comparison  with  any  line  measures  then  obtainable. 

To  those  who  have  grown  up  with  micrometers  in  their  hands, 
so  to  speak,  it  is  difficult  to  understand  the  mental  attitude 
toward  this  subject  which  prevailed  prior  to  the  introduction 
of  the  micrometer.  With  their  calipers  mechanics  had  been 
habitually  repeating  sizes  with  an  accuracy  exceeding  a  thou- 
sandth of  an  inch  but,  without  the  micrometer,  they  had  no 
means  of  determining  the  limits  to  which  they  were  actually 
working  and  the  thousandth  of  an  inch  as  an  actual  dimension 
was  looked  upon  with  derision.  Under  such  conditions  Whit- 
worth's  deliberate  setting  out  to  measure  minute  differences 
that  could  be  felt  but  not  seen,  seemed  almost  like  attempting 
to  weigh  a  shadow.  Starting  with  this  mental  conception  of 
minute  quantities,  Whitworth  made  the  thousandth  of  an  inch 
a  common-place,  the  ten  thousandth  a  tangible  reality,  and  the 
hundred  thousandth  something  more  than  a  philosophical 
abstraction. 

Whitworth  believed,  erroneously,  that  he  had  proven  end 
measures  to  be  more  accurate  than  line  measures,  even  when 
the  latter  were  used  with  a  microscope  and,  through  his  plug 
and  ring  gages,  he  proposed  the  abandonment  of  line  and  the 
substitution  of  end  measures  in  machine  construction.  This  is 
exactly  what  has  been  done  in  the  manufacturing  system  and, 
in  view  of  the  conditions  that  obtained  in  Whitworth's  time, 
the  conception  was  nothing  less  than  brilliant.  In  this,  as  in 
so  many  other  things,  he  was  decades  ahead  of  the  rest  of  the 
world. 


84  METHODS  OF  MACHINE  SHOP  WORK 

The  only  limitation  that  can  be  placed  upon  admiration  for 
Whitworth's  work  grows  out  of  the  fact  that  the  real  accuracy 
of  his  gages  was  far  behind  the  claims  made  for  it.  Measure- 
ments of  the  Whitworth  plugs  shown  in  Fig.  50,  by  Mr.  Bond 
have  shown  errors  that  are  irreconcilable  with  the  old  claims. 
Moreover,  gages  imported  by  different  parties  were  found,  when 
compared,  not  to  agree,  and  even  gages  of  the  same  set  were 
found  to  be  inconsistent — two  plugs  placed  side  by  side  being 
found  to  overfill  or  to  fail  to  fill  a  ring  which  was  nominally 
their  sum.  Nothing  is  better  established  than  the  fact  that 
the  early  Whitworth  gages  fell  far  below  the  claims  made  for 
them. 

No  explanation  of  this  has  ever  been  made.  The  critic 
should,  however,  remember  that  it  is  manifestly  unfair  to  judge 
pioneer  work  by  the  standard  of  ultimate  achievement.  The 
only  proper  comparison  is  one  that  measures  the  progess  made 
and,  when  judged  by  this  standard,  Whitworth's  work  is  found 
to  be  revolutionary.  Whatever  may  be  said  regarding  the 
failure  of  his  gages  to  meet  specifications,  it  may  at  least  be  said 
that  it  is  not  to  his  discredit  that  he  aimed  at  a  mark  beyond 
his  reach,  nor  that  he  left  something  for  others  to  do,  even 
though  that  something  was  the  placing  of  the  keystone  of  the 
arch. 

The  beginning  of  accurate  shop  measurements  in  the  United 
States,  as  has  already  been  said,  was  by  Dr.  John  E.  Sweet 
at  Cornell  University,  who  completed  a  measuring  machine, 
shown  in  Fig.  57,  in  1874.  The  screw  of  this  machine  has  16 
threads  per  inch  and  its  divided  circle  has  625  divisions,  the 
readings  being  thus  to  the  ten  thousandth  of  an  inch.  The 
machine  has  several  features  which  are  now  universal  in  such 
machines:  It  stands  upon  three  legs,  its  screw  is  of  the  ratchet 
section  and  the  screw  and  nut  are  of  the  same  length,  thus 
eliminating  local  wear. 

The  machine  was  made  before  Whitworth's  dictum  regard- 
ing the  superiority  of  end  measures  had  been  overthrown  and 
it  is  thus  an  end-measure  machine.  Accompanying  it  were  a 
series  of  end-measure  rods  differing  by  whole  inches.  By  the 
use  of  these  rods,  one  of  which  is  shown  in  the  illustration,  the 


MEASURES  OF  LENGTH  85 

tail  stock  was  adjusted  for  the  whole  inches,  the  fractions 
being  determined  by  the  turning  of  the  screw.  The  necessity 
of  nicety  of  adjustment  of  the  tail  stock  was,  however,  elimi- 
nated by  the  adjustable  zero  bar  which  may  be  turned  about 
the  screw  to  match  the  position  of  the  zero  on  the  divided 
circle  wherever  it  may  happen  to  fall — a  feature  which,  also, 
is  found  in  more  recent  machines. 


FIG.  57. — Cornell  University  measuring  machine. 

MODERN  MEASURING  MACHINES 

In  all  measuring  machines,  next  to  accuracy  of  parts,  the  chief 
problem  is  the  finding  of  means  by  which  to  secure  uniform 
pressure  of  contact.  The  means  adopted  in  this  machine 
for  this  purpose — and  it  was,  perhaps,  the  least  satisfactory 
feature  of  the  machine1 — was  that  of  friction  between  the  cross 
bar  in  front  of  the  divided  wheel  and  the  face  of  the  wheel. 
The  chief  differences  between  various  makes  of  measuring  ma- 
chines are  at  this  point  and  the  leading  methods  adopted  are 
hence  given  in  connection  with  the  descriptions  of  the  following 
machines. 

The  Brown  and  Sharpe  Machine — due  to  O.  J.  Beale — - 
which  is  a  development  of  the  original  machine  made  in  1878, 
is  shown  in  Fig.  58.  Its  most  striking  feature  is  the  remark- 

1  That  is,  for  the  degree  of  precision  aimed  at.  For  micrometers  reading  to 
thousandths  the  device  is  entirely  satisfactory. 


86 


METHODS  OF  MACHINE  SHOP  WORK 


ably  massive  bed  which  is  of  box  form  and  eighteen  inches 
deep.  The  machine  is  a  bold  and  original  application  of  the 
principle  of  the  increase  of  sensitiveness  due  to  increased  stiff- 
ness which  is  explained  at  the  beginning  of  the  chapter  on  gages. 
With  its  massive  bed  the  sensitiveness  of  simple  touch  is  so 
greatly  increased  that  dependence  is  placed  upon  it  alone,  and 
by  it  the  hundred  thousandth  of  an  inch  is  easily  detected. 

This  does  not  eliminate  the  personal  equation  and,  were  the 
machine  put  into  the  hands  of  miscellaneous  users,  differences 
of  measurement  due  to  differences  of  pressure  would  arise. 
The  machine  is  not,  however,  so  used.  It  is  not  made  for  sale, 


FIG.  58. — Brown  and  Sharpe  measuring  machine. 

being  used  only  in  the  gage  department  of  the  Brown  &  Sharpe 
works  where  the  machines  are  used  by  none  but  trained  men  and 
under  these  conditions  the  readings  are  entirely  satisfactory. 
This  was  the  first  machine  in  which  the  authority  of  Whitworth 
as  regards  the  superiority  of  end  over  line  measures  was  dis- 
puted and  the  line-measure  rehabilitated  and  placed  where 
it  belongs  as  the  ultimate  standard.  While  end-measure  ma- 
chines are  still  made,  the  line-measure  machine  is  much  more 
common.  The  line  measure  of  this  machine  is  engraved  on 
the  long  tail  stock  spindle,  of  which  the  upper  half  is  cut  away 
in  order  to  bring  the  scale  at  the  center  line  of  the  machine,  a 


MEASURES  OF  LENGTH 


87 


FIG.  59. — Rear  side. 


FIG.  60. — Front  side. 
Pratt  and  Whitney  measuring  machine. 


88  METHODS  OF  MACHINE  SHOP  WORK 

microscope  being  provided  for  reading  it.  In  this  location  of 
the  scale  the  machine  is  unique.  The  lever  action  due  to  the 
position  of  the  measuring  fingers  above  the  bed  causes  the 
fingers  to  change  position  with  flexure  of  the  bed  and  the  ar- 
rangement described  was  adopted  in  order  to  provide  for 
this  effect. 

The  Pratt  and  Whitney  machine — due  to  Professor  Rogers 
and  G.  M.  Bond — is  shown  in  Figs.  59  and  60. 1  The  line 
measure,  which  is  divided  into  whole  inches  only,  fractional 
readings  being  obtained  from  the  screw,  is  seen  lying  on  the 
bed  in  Fig.  59  together  with  the  microscope  for  reading  it 
attached  to  the  moving  head  stock. 

Uniform  pressure  of  contact  is  secured  by  means  of  a  gravity 
drop  piece.2  This  device,  which  is  clearly  shown  in  the  tail 
stock  of  Fig.  60,  is  a  small  cylinder  of  hardened  steel,  precisely 
like  a  plug  gage,  which  is  pinched  between  two  opposing  fingers. 
One  of  these  fingers  is  attached  to  the  frame  of  the  tail  stock  and 
the  other  to  an  arm  projecting  from  the  spindle  of  the  tail 
stock — a  spring  behind  the  spindle  maintaining  pressure  suf- 
ficient to  hold  the  gravity  piece  in  a  horizontal  position.  When 
making  a  measurement  the  measuring  screw  is  turned  until 
this  gravity  piece  drops  to  a  vertical  position  like  a  semaphore, 
but  without  dropping  out.  This  machine  was  intended  for 
sale  and  it  has  gone  to  all  quarters  of  the  globe  where  such 
machines  are  needed.  It  was,  in  fact,  this  machine  which 
first  carried  means  for  making  independent  measurements  of 
high  precision  into  the  workshops  of  the  world. 

The  measuring  machine  of  the  [British]  Newall  Engineering 
Company — due  to  J.  E.  Story — is  shown  in  Fig.  61.  The 
method  of  obtaining  uniform  pressure  of  contact  is  by  the  use  of 
a  sensitive  level  swiveled  upon  the  tail  stock  casting  and  having 
a  short  arm  projecting  from  its  lower  side,  against  which  the 
spindle  of  the  tail  stock  abuts,  a  light  spring  pushing  the  spindle 
forward.  The  construction,  which  is  shown  more  fully  in  Fig. 

1  The  machine  shown  is  not  in  all  respects  of  the  most  recent  pattern.     The 
illustrations  shown  are  chosen  because  they  show  the  desired  features  most 
clearly. 

2  This  device  was  used  by  Whitworth  in  his  millionth  measuring  machine. 


MEASURES  OF  LENGTH  89 

62,  multiplies  the  spindle  movements,  as  read  by  the  bubble  of 
the  level,   by  about  four  thousand.      The  machine  shown  is 


FIG.  61. — Newall  measuring  machine. 

fitted  with  a  line  measure  and   microscope,  but  end-measure 
machines  are  also  made. 


FIG.  62. — Contact  feature  of  the  Newall  measuring  machine. 

Another  refinement  of  this  machine  is  found  in  the  construc- 
tion of  the  head  stock.     In  previous  machines  the  measuring 


90 


METHODS  OF  MACHINE  SHOP  WORK 


screw  acts  not  only  to  traverse  itself  but  as  a  bearing  to  carry 
its  own  weight  and  that  of  the  graduated  wheel.  In  this  ma- 
chine the  shank  of  the  screw  is  extended  at  each  end  to  form 
bearings  which  support  the  weight  of  the  parts,  relieving  the 
screw  of  that  duty  and  leaving  to  it  the  traverse  function  only. 
The  arrangement  will  be  recognized  as  an  application  of  the 
principle  of  the  division  of  functions.  It  is  shown  in  Fig.  63. 


FIG.  63. — Section  of  headstock  of  the  Newall  measuring  machine. 

THE  MICROMETER  CALIPER 

The  micrometer  caliper,  which  was  first  made  an  article  of 
commerce  by  the  Brown  and  Sharpe  Manufacturing  Company 
in  1867,  is  essentially  a  small  portable  measuring  machine.  Just 
as  the  Pratt  and  Whitney  measuring  machine  has  been  the  means 
of  carrying  precision  measurements  of  the  grade  required  into 
the  tool  rooms  of  the  world,  so  the  Brown  and  Sharpe  micrometer 
caliper  has  performed  the  same  office  for  the  commercial  de- 
partments of  machine  construction.  It  has  also  been  the 
greatest  of  all  educators  in  the  matter  of  what  really  constitutes 
accuracy.  It  is  made  in  a  great  variety  of  forms  and  for  both 
inside  and  outside  measurements. 

The  range  of  adjustment  of  the  measuring  screw  is  uniformly 
one  inch.  The  tail  spindle  or  anvil  of  large  instruments  is 
sometimes  adjustable  by  means  of  end-measure  rods  of  even 
inch  lengths,  by  which  the  range  of  the  instrument  is  made 
to  cover  several  inches,  and  this  anvil  is  sometimes  permanent, 
the  range  in  such  instruments,  whatever  their  capacity,  being 
one  inch  only.  A  set  of  micrometers  of  the  latter  construction 
by  the  J.  T.  Slocomb  Company  is  shown  in  Fig.  64.  In  the 
base  of  the  frame  which  carries  the  micrometers  is  a  set  of  end- 


MEASURES  OF  LENGTH 


91 


FIG.  64. — Set  of  Slocomb  micrometer  calipers. 


FIG.  65. — Set  of  Brown  and  Sharpe  inside  micrometer  calipers. 


92  METHODS  OF  MACHINE  SHOP  WORK 

measure  rods  by  which  to  verify  and,  if  necessary,  correct  the 
accuracy  of  the  instruments,  for  which  purpose  the  anvil  screws 
are  adjustable  through  a  slight  distance.  Fig.  65  shows  a  set 
of  inside  micrometers  by  the  Brown  and  Sharpe  Manufactur- 
ing Company.  In  these,  as  in  the  outside  instruments,  the 
range  of  the  screw  is  uniformly  one  inch.  Micrometer  heads 
without  frames  or  other  attachments  are  also  provided  and 
have  many  applications  in  connection  with  special  gages  of 
various  kinds.  Such  micrometer  heads  are  seen  in  the  large 
Westinghouse  micrometer  calipers  of  Figs.  93  and  94  and  in 
the  machine  for  measuring  the  errors  of  pitch  of  long  screws, 
Fig.  116. 

PRECISION  SCREWS  AND  PRECISION  LATHES 

All  of  these  measuring  machines  depend  upon  a  screw  for  their 
readings  and  it  is  apparent  that  this  screw  must  be  of  precision 
grade  and  be  cut  on  a  precision  lathe.  The  lathes  with  which 
measuring-machine  screws  are  cut  have  not  been  published  and 
in  their  stead  are  given  two  others. 

While  methods  have  been  devised  for  that  purpose,  screws  are 
seldom  originated  in  the  sense  that  flat  surfaces  are  originated. 
In  the  production  of  precision  screws  the  procedure  is  to  take 
the  best  screw  available  as  a  starting  point,  measure  its  errors 
and  then  adopt  means  by  which,  although  this  screw  is  used  as  a 
lead  screw,  its  errors  do  not  appear  in  the  screws  cut  from  it. 

To  the  best  of  the  author's  knowledge  there  is  but  one  method 
of  doing  this  which  is  shown  with  great  clearness  in  the  illus- 
tration, Fig.  66,  of  Professor  Rogers's  precision  lathe.1  The 
first  thing  to  be  observed  about  this  lathe  is  its  massiveness. 
The  slabs  which  form  the  shears  of  the  machine  were  two  and  a 
half  inches  thick  and  the  other  parts  of  corresponding  massive- 
ness.  The  liberal  use  of  mass  was,  in  fact,  one  of  the  cardinal 
points  of  all  of  Professor  Rogers's  work. 

In  order  to  get  rid  of  the  tendency  to  slew  the  tool  carriage, 
due  to  the  customary  location  of  the  lead  screw  in  front  of  the 

1  The  lathe,  which  was  made  by  Webber  and  Philbrick,  was  destroyed  by  fire 
shortly  before  the  death  of  Professor  Rogers. 


MEASURES  OF  LENGTH 


93 


machine,  that  screw  was  in  this  machine  placed  within  the  shears 
and  vertically  below  the  center  line  of  the  centers.  Carried  by 
the  slide  rest  is  a  microscope  which  is  used  to  read  aline  measure, 
divided  into  inches,  which  lies  upon  the  rear  side  of  the  lathe  bed. 
The  microscope  contains,  of  course,  an  eye-piece  micrometer. 


FIG.  66. — Professor  Rogers's  precision  lathe. 

A  slab-shaped  piece  of  iron  will  be  seen  upon  the  front  side  of 
the  lathe,  to  which  is  bolted  a  templet  of  irregular  outline. 
The  center  of  curvature  of  the  slab,  as  seen  endwise,  is  at  the 
center  of  the  lead  screw.  The  nut  which  engages  the  screw  has 
no  rigid  connection  with  the  carriage — being  what  Professor 
Rogers  called  a  free  nut  which  traverses  the  carriage  by  pushing 
it.  The  nut  is  also  free  to  turn  about  the  screw  and  has  attached 
to  it  a  curved  lever  which  reaches  over  the  lathe  shear  and  carries 
at  its  outer  end  a  roller  which  rides  on  the  correction  templet. 


94  METHODS  OF  MACHINE  SHOP  WORK 

It  is  obvious  that  as  the  carriage  advances  the  lever  will  rise 
and  fall  on  this  templet,  turning  the  nut  with  it  and  thereby 
hastening  or  retarding  the  advance  of  the  carriage  as  the  case 
may  be.  It  is  this  hastening  and  retarding  of  the  action  of  the 
screw  which  corrects  the  errors  of  the  screw,  the  outline  of  the 
templet  being  such  as  to  accomplish  this  result.1 

In  the  determination  of  this  outline  the  divided  scale  was  ad- 
justed lengthwise  until  one  of  its  lines  was  split  by  the  cross  hair 
of  the  microscope.  The  driving  pulley  was  then  turned  such  a 
number  of  turns  as  would,  assuming  the  screw  to  be  correct, 
advance  the  carriage  one  inch.  Reading  the  division  of  the 
scale  through  the  microscope,  if  the  cross  hair  and  division  line 
did  not  agree,  the  lever  attached  to  the  nut  was  raised  or  lowered 
until  the  cross  hair  and  line  did  agree,  thereby  locating  a  point 
of  the  templet.  This  process  was  then  repeated  for  the  next 
inch  division  of  the  scale  and  so  on  to  the  end,  thus  obtaining 
a  series  of  points  in  the  outline  of  the  templet  through  which, 
a  smooth  curve  being  drawn,  the  outline  of  the  templet  was  de- 
termined and  made.  This  being  done  and  the  roller  upon  the 
end  of  the  lever  being  placed  in  position,  it  is  clear  that,  in  the 
action  of  the  lathe,  the  turning  of  the  nut  due  to  the  rise  and  fall 
of  the  lever  on  the  templet  would  compensate  the  errors  of  the 
screw  when  cutting  another. 

The  gears  at  the  end  of  the  lathe  are  of  the  same  size  because 
the  lathe  was  not  intended  to  cut  screws  of  other  pitches  than 
that  of  the  lead  screw.  To  attempt  to  do  this  would  introduce 
errors  due  to  the  irregular  spacing  of  the  teeth  of  different  gears 
which  it  would  be  impossible  to  compensate.  With  the  gears 
shown  it  is  obvious  that  the  errors  determined  in  outlining  the 
templet  are  the  combined  errors  of  the  screw  and  gears,  and,  once 
determined,  it  is  only  necessary  to  keep  the  gears  on  the  lathe 
permanently  or,  if  removed,  to  replace  them  in  the  same  relative 
positions  in  order  to  insure  the  continued  correctness  of  the 
corrections.  As  a  matter  of  fact,  after  the  errors  were  deter- 
mined the  gears  were  marked  so  as  to  insure  their  future 

1  Professor  Rogers  obtained  the  method  from  M.  Froment  of  the  French  firm 
Dumoulin  and  Froment,  makers  of  optical  and  scientific  apparatus. 


MEASURES  OF  LENGTH 


95 


replacement  in  the  same  relative  positions  in  case  it  was  found 
desirable  to  remove  them. 

Figs.  67-69  show  the  precision  lathe  of  the  National  Physical 
Laboratory  of  Great  Britain  which  employs  the  same  device  for 
correcting  the  error  of  the  screw  as  Professor  Rogers's  lathe,  but 


FIG.  67. — Precision  lathe  of  the  British  National  Physical  Laboratory. 

which  is  in  many  other  respects  far  superior  to  it.  Among  these 
may  be  noted  the  support  of  the  machine  upon  three  points  and 
by  a  suitably  trussed  sub-frame  casting;  the  provision  of  a  tubular 
bed  which,  in  torsion,  is  enormously  stiffer  than  any  other 
possible  section,  and  the  provision  of  separate  nut  and  tool 


FIG.  68. — Nut  carriage 


'^.  -L^UU      LC1.J.  llCL^l^.  JL    J.*JT«        WU. J. 

Section  of  the  precision  lathe  shown  in  Fig 


FIG.  69. — Tool  carriage 


Fig.  67. 

carriages  connected  by  massive  rods  in  direct  tension  only, 
whereby  the  lead  screw  and  the  screw  in  process  of  being  cut  are 
placed  in  line  with  one  another.  As  originally  made  the  ma- 
chine was  provided  with  an  independent  driving  head  and  an 
equalizing  driver  of  which  portions  are  shown  in  Fig.  67,  whereby 


96  METHODS  OF  MACHINE  SHOP  WORK 

the  pull  of  the  belt  on  the  machine  was  eliminated.  As  now 
used,  however,  the  lathe  is  driven  by  hand.  Its  only  use  is  to 
finish  screws  which,  except  for  the  correcting  cut,  are  made  on 
other  lathes. 

The  correcting  bar  is  plainly  seen  in  Fig.  67  while  Fig.  68, 
which  is  a  section  through  the  nut  carriage,  shows  the  same 
bar  at  a  and  in  addition  the  tubular  bed.  Fig.  69  is  a  section 
of  the  tool  carriage  and  shows  the  support  of  the  screw  being 
cut  and  the  fact  that  the  cutting  tool  is  inverted  from  the  usual 
position,  this  arrangement  being  adopted  because  believed  to 
be  more  conducive  to  the  avoidance  of  chatter.  Screws 
have  been  cut  with  this  lathe  of  which  the  errors  are  less  than 
the  ten  thousandth  of  an  inch  in  twelve  inches  of  length.  It 
represents  the  culmination  of  the  solution  of  the  fascinating 
precision  screw  problem  which  has  engaged  the  attention  of 
many  mechanics  from  Maudsley  down,  including  Whitworth. 


CHAPTER  IV 

THE  MEASUREMENT  OF  ERRORS 

Instruments  for  measuring  errors  embodying  the  multiplying  lever — 
Uses  of  these  instruments— The  dial  gage  and  its  uses — The  measure- 
ment of  errors  with  extemporized  apparatus. 

In  a  large  number  of  cases  of  measurement  the  thing  measured 
is  the  error  from  truth.  This  error  may  be  the  error  from 
truth  of  size,  in  which  case  the  process  of  measurement  is  one 
of  comparison  with  a  standard,  the  measuring  instrument  giv- 
ing the  difference  between  the  standard  and  the  piece  which 
is  compared  with  it.  In  other  cases  the  error  measured  is  one 
of  position  or  adjustment,  in  which,  for  example,  the  degree 
of  parallelism  or  of  squareness  of  one  piece  with  another  is 
determined.  For  both  these  classes  of  measurement  instru- 
ments embodying  the  multiplying  lever  possess  advantages  over 
the  micrometer  because  less  time  is  required  for  their  use  and 
the  personal  equation  is  eliminated. 

APPLICATIONS  OF  THE  MULTIPLYING  LEVER 

An  application  of  the  multiplying  lever  to  the  comparison 
of  parts  with  a  standard  is  shown  in  Figs.  70  and  71  from 
the  Canadian  Ingersoll-Rand  Company.  The  standard  with 
which  the  comparison  is  made  may  be  a  gage  or,  as  in  this  case, 
a  sample  piece  preserved  as  a  standard.  The  illustrations 
show  an  indicating  beam  caliper  made  by  the  Syracuse 
Twist  Drill  Company  in  the  act  of  gaging  a  rock  drill  slide  valve, 
Fig.  70  showing  the  instrument  as  it  actually  appears  and  Fig. 
71  with  a  protecting  cover  removed  in  order  to  show  the  con- 
struction. The  stationary  head  of  the  instrument  carries  a 
multiplying  lever  which  plays  over  a  graduated  scale  at  the 
top,  the  graduations  reading  to  thousandths.  The  short  end 
of  the  lever  is  connected  with  the  measuring  finger,  which  has  a 
7  97 


98 


METHODS  OF  MACHINE  SHOP  WORK 


FIG.  70. — With  cover  plate  in  position. 


FIG.  71. — With  cover  plate  removed. 
Indicating  beam  caliper. 


THE  MEASUREMENT  OF  ERRORS  99 

slight  endwise  movement.  The  sliding  head  carries  a  second 
finger  which  is  threaded  and  fitted  with  a  knurled  head.  The 
standard — an  end-measure  rod  or  a  sample  piece  preserved 
as  a  standard,  as  in  the  present  instance — is  placed  in  position 
and  the  finger  upon  the  moving  head  is  adjusted  until  the 
multiplying  lever  stands  at  the  zero  of  the  scale,  this  zero  be- 
ing at  the  center  of  the  scale  in  order  to  read  errors  in  both 
directions.  This  being  done,  the  parts  as  made  are  placed  in 
position  and  their  correctness  or  their  errors  are  determined 
at  once. 

This  is  the  cheapest  method  known  to  the  author  of  intro- 
ducing the  limit  gage  system.  The  limits  are  tabulated  and  the 
inspector  has  only  to  compare  them  with  the  readings  of  the 
instrument  in  order  to  determine  if  the  parts  are  within  the 
limits.  The  instrument  has  received  far  less  application  than 
it  deserves  and  this  is  the  more  strange  because  of  the  wide 
application  of  the  multiplying  lever  to  other  uses.  It  will  be 
observed  that  the  instrument  is  in  no  sense  a  measuring  instru- 
ment. It  is  a  comparator,  that  is  to  say,  it  compares  parts  and 
determines  their  differences  but  it  does  not  determine  their 
absolute  sizes. 

THE  TOOL-MAKER'S  INDICATOR 

The  widest  application  of  the  multiplying  lever  is  to  the  tool- 
maker's  indicator,  one  of  which,  by  Koch  &  Son,  is  shown  in 
Fig.  72,  of  which  the  lower  view  shows  the  sliding  cover  removed 
and  the  multiplying  levers  exposed.  Such  indicators  appear 
in  a  great  variety  of  forms  as  they  are  frequently  home  made. 
The  present  instrument  is  unusual  in  that  it  is  fitted  with 
compound  levers,  thereby  making  it  extremely  compact. 
These  levers  are  enclosed  in  a  steel  box  which  has  at  each  end 
a  projecting  finger  which  engages  with  the  short  end  of  the 
lever  system.  The  finger  at  the  left  slides  endwise  while  the 
one  at  the  right  is  a  bell  crank,  its  external  movement  being 
vertical  in  the  position  shown.  Great  flexibility  of  adjustment 
is  thus  made  possible,  including  internal  readings  by  entering 
the  bell  crank  end  into  holes  to  be  indicated. 

The   applications    of    this   instrument   are    almost    endless. 


100  METHODS  OF  MACHINE  SHOP  WORK 

Perhaps  the  most  common  is  to  the  centering  of  work  in  the 
lathe,  as  illustrated  in  Fig.  73,  in  which  the  vibration  of  the 
lever  as  the  lathe  revolves  shows  the  amount  of  untruth  of  the 
piece  of  work.  Fig.  74  shows  the  adjustment  of  a  milling 
machine  vise  at  right  angles  with  the  cutter  arbor  to  which 
latter  the  indicator  is  clamped  by  a  series  of  collars  and  a  bind- 
ing nut.  By  traversing  the  work  table  the  indications  of  the 
instrument  indicate  any  lack  of  truth  of  the  vise  jaws.  Fig. 
75  shows  the  instrument  used  for  transferring  a  measurement 
to  an  otherwise  inaccessible  place.  The  height  from  the  sur- 


FIG.  72. — Tool-maker's  indicator. 

% 

face  plate  is  taken  in  the  indicator  from  the  height  gage,  when 
the  indicator  is  lifted  over  the  jig  body  into  which  the  measur- 
ing finger  enters.  The  position  of  a  point  within  the  jig  may 
then  be  compared  with  the  reading  of  the  height  gage.  Fig. 
76  shows  the  application  of  an  instrument  of  different  pattern 
to  the  adjustment  of  a  swivel ed  angle  plate.  The  small  angle 
plate  clamped  to  the  swiveled  plate  being  known  to  be  accu- 
rate, it  is  obvious  that  by  sliding  the  indicator  and  its  base 
about  the  horizontal  surface  plate,  the  parallelism  of  the  small 
plate  and  the  perpendicularity  of  the  swiveled  plate  with  the 
large  plate  are  determined. 


THE  MEASUREMENT  OF  ERRORS 


101 


102 


METHODS  OF  MACHINE  SHOP  WORK 


a, 
-d 


i. 

to 


THE  MEASUREMENT  OF  ERRORS 


103 


MEASURING  ACCURACY  OF  POSITION 

Applications  of  the  multiplying  lever  to  the  determination 
of  accuracy  of  position  are  shown  in  Figs.  77  and  78,  from  the 
Cadillac  automobile  works.  In  Fig.  77  the  parallelism  of  the 
crank  pin  and  piston  pin  bearings  of  a  connecting  rod  is  being 
tested.  The  crank  pin  bearing  is  clamped  upon  a  true  arbor 
a  which  is  mounted  in  suitable  supports,  the  piston  pin  end 
having  inserted  within  it  a  similar  true  arbor  b.  A  slide 
may  be  reciprocated  a  short  distance  by  the  hand  lever  d  and 


FIG.  79. — Testing  accuracy  of  spacing  of  worm  wheel  teeth. 

a  swiveled  lever  e  carried  by  the  slide  c  be  thus  brought  into 
contact  with  the  arbor  b.  A  multiplying  lever  /  plays  over  a 
graduated  scale  at  its  left-hand  end  and  thus  shows  any  de- 
parture from  parallelism  of  the  two  arbors. 

In  Fig.  78  the  squareness  of  the  piston  with  the  crank-pin  hole 
is  similarly  tested  after  the  parts  have  been  assembled.  The 
crank-pin  bearing  is  clamped  upon  the  pin  a  and  the  slide  at 
the  right  is  adjusted  until  the  swiveled  lever  b  makes  contact 
with  the  piston.  Two  multiplying  levers  c,  d,  of  which  the  lat- 
ter plays  over  a  graduated  scale  at  its  further  end,  show  any 
lack  of  truth,  suitably  magnified. 


104 


METHODS  OF  MACHINE  SHOP  WORK 


Silver. 


.Spider 


Figs.  79  and  80,  from  the  Cincinnati  Milling  Machine  Co., 
show  an  application  of  the  multiplying-lever 
principle  to  the  determination  of  the  accuracy 
of  the  spacing  of  the  teeth  of  the  worm  wheel 
of  a  milling  machine  dividing  head.  The 
multiplying  lever  is  forked  at  its  lower  end, 
as  shown  more  clearly  in  Fig.  80,  and  at  its 
upper  end  it  carries  a  spider-web  line  which 
is  read  against  a  line  upon  a  silver  disc  at- 
tached to  the  frame.  Going  back  to  Fig.  79, 
the  arbor  upon  which  the  worm  gear  to  be 
tested  is  mounted  carries  on  its  rear  end  an 
accurately  divided  circle  by  which  the  worm 
wheel  may  be  turned  through  the  spaces  cor- 
responding with  the  intended  spacing  between 
the  teeth.  Were  this  spacing  correct,  it  is 
clear  that  the  spider-web  line  and  the  line 
upon  the  silver  disc  would  agree  for  every 
tooth  and  that  the  errors  will  be  shown  by  a 
lack  of  such  agreement.  The  degree  of  pre- 
cision of  the  equipment  is  sufficiently  indi- 
cated by  the  fact  that  both  graduated  circle  and  hair  lines  are 
read  by  microscopes. 


FIG.  80. — Indicator 
of  worm  wheel  test- 
ing apparatus. 


THE  DIAL  GAGE  AND  ITS 
APPLICATIONS 

A  modification  of  the  multiplying- 
lever  principle  which  has  many  appli- 
cations is  found  in  the  dial  gage  of 
the  B.  C.  Ames  Company,  shown  in 
Fig.  81.  In  this  instrument  the 
movement  of  the  measuring  finger  is 
shown  by  the  turning  of  the  index 
on  the  dial,  the  two  being  connected 
by  multiplying  internal  mechanism 
not  shown.  In  the  instrument 
shown  the  readings  are  to  thou- 
sandths which  are  numbered  from  o  to  50  in  each  direction,  as 


FIG.  81. — Dial  test  indicator. 


THE  MEASUREMENT  OF  ERRORS 


105 


FIGS.  82  and  83. — Testing  the  squareness  of  planer  housings. 


106  METHODS  OF  MACHINE  SHOP  WORK 


FIGS.  84  and  85. — Testing  the  squareness  of  a  milling  machine  knee. 


THE  MEASUREMENT  OF  ERRORS 


107 


errors  are  as  apt  to  lie  in  one  direction  as  the  other.  The  dial 
may  be  turned  to  bring  the  zero  under  the  index  wherever  it 
may  happen  to  lie  at  the  first  reading.  This  adjustment, 
combined  with  the  increased  range  of  the  instrument,  makes 
it  more  convenient  for  many  purposes  than  the  lever  con- 
struction previously  shown. 

Figs.  82  and  83,  from  the  American  Tool  Works  Company, 
show  the  instrument  used  in  combination  with  a  square.  By 
moving  the  indicator  and  the  block  to  which  it  is  attached 


FIG.  86. — Testing  the  parallelism  of  a  radial  drilling  machine  arm  and  base  and 
the  squareness  of  the  spindle  with  the  base. 

vertically,  it  is  obvious  that  the  degree  of  squareness  of  the 
planer  housings  with  the  V's  of  the  bed  in  both  directions  is 
quickly  determined.  Similarly  Figs.  84  and  85,  from  the 
Cincinnati  Milling  Machine  Company,  show  applications  to 
milling-machine  construction.  In  Fig.  84  the  squareness  of 
the  knee  with  the  main  frame  as  seen  in  plan,  and  in  Fig.  85 
as  seen  in  elevation,  is  determined.  The  errors  found  are 
removed  by  scraping. 


108  METHODS  OF  MACHINE  SHOP  WORK 


FIG.  87. — Testing  the  alignment  of  a  milling  machine  spindle. 


FIG.  88. — Testing  the  alignment  of  the  spindle  of  a  milling  machine  dividing  head. 


FIG.  89. — Testing  the  alignment  of  milling  machine  centers. 


THE  MEASUREMENT  OF  ERRORS  109 

Fig.  86,  also  from  the  American  Tool  Works  Company,  shows 
applications  that  are  typical  of  many.  The  indicator  is  attached 
to  an  arm  seen  endwise  but  extending  radially  from  an  arbor 
inserted  in  a  radial  drilling  machine  spindle.  By  traversing 
the  head  along  the  arm  and  taking  readings  at  various  points 
indicated  by  the  three  circles  at  the  front  of  the  base,  the  error 
in  the  parallelism  of  arm  and  base  is  determined.  Similarly  by 
revolving  the  spindle  and  taking  readings  at  the  four  points 
indicated  by  the  circles,  the  squareness  of  the  spindle  with  the 
base  is  determined. 

Fig.  87,  from  the  Cincinnati  Milling  Machine  Company, 
shows  an  application  to  the  testing  of  the  alignment  of  a  milling- 
machine  spindle  and  work  table.  The  test  arbor,  which  is 
inserted  in  the  taper  hole  of  the  machine  spindle,  being  known 
to  be  true,  it  is  only  necessary  to  revolve  the  spindle  in  order 
to  show  any  lack  of  truth  of  the  hole  since  such  lack  of  truth 
will  cause  the  arbor  to  vibrate  and  this  vibration  will  appear 
in  the  movements  of  the  indicator  pointer.  Similarly  by  mov- 
ing the  indicator  and  stand  to  the  inner  end  of  the  arbor,  any 
lack  of  parallelism  of  arbor  and  work  table  will  be  shown,  and, 
again,  by  traversing  the  work  table  on  the  knee,  lack  of  par- 
allelism between  the  arbor  and  the  knee  will  appear. 

Fig.  88,  from  the  same  source  as  the  preceding  illustra- 
tion, shows  a  similar  application  to  the  taper  hole  of  the  work 
spindle  of  a  milling-machine  dividing  head.  After  the  truth 
of  the  hole  has  been  proven,  the  head  may  be  adjusted  on  its 
swivel  until  the  readings  show  the  arbor  to  be  parallel  with  the 
base,  when  the  zero  of  the  graduated  arc  for  reading  the 
angle  of  elevation  may  be  located,  or,  if  already  located, 
its  truth  may  be  proven.  Still  another  application  appears  in 
Fig.  89  in  which  the  base  of  the  stand  for  the  indicator  has 
a  tongue  which  drops  into  the  T-slot  of  the  main  base.  The 
head  and  tail  stocks  have  similar  tongues  and,  the  arbor  be- 
ing known  to  be  true,  traverse  of  the  indicator  in  the  slot 
will  show  the  truth  of  the  alignment  of  the  live  and  dead 
centers. 

These  illustrations  indicate  the  degree  of  precision  that 
enters  into  the  construction  of  modern  machine  tools. 


110 


METHODS  OF  MACHINE  SHOP  WORK 


TESTS  WITH  EXTEMPORIZED  APPARATUS 

A  large  number  of  entirely  satisfactory  tests  may  be  made 
with  extemporized  apparatus  and  an  ordinary  micrometer 
caliper  by  measuring  from  the  rear  end  of  the  barrel.  Figs. 
90-92  show  such  tests  of  the  accuracy  of  a  lathe.  Putting  a 
well-centered  arbor  in  the  lathe  and  mounting  a  micrometer 
upon  it,  as  in  Fig.  90,  and  taking  readings  against  the  face 
plate  at  the  ends  of  the  vertical  and  horizontal  diameters,  it 


FIG.  90. 


FIG.  91.  FIG.  92. 

Extemporized  tests  with  micrometer  calipers. 

is  clear  that  the  squareness  of  the  plate  and  with  it  the  align- 
ment of  the  live  spindle  with  the  line  of  centers  may  be  de- 
termined. Again  by  mounting  the  calipers  as  shown  in  Fig. 
91,  taking  a  reading  with  the  tail  spindle  drawn  in,  then  loosen- 
ing the  tail  stock  upon  the  bed,  running  out  the  tail  spindle 
and  repeating  the  reading,  the  horizontal  alignment  of  the 
tail  spindle  with  the  line  of  centers  may  be  determined.  Again, 
mounting  the  caliper  as  in  Fig.  92  and  repeating  the  operations 
just  described,  the  vertical  alignment  of  the  tail  spindle  may  be 
determined. 


CHAPTER  V 
GAGES 

Relation  of  stiffness  and  sensitiveness  of  gages — In  large  gages  stiffness 
must  be  sacrificed  to  lightness — Expedients  used  under  these  conditions — 
Defects  of  snap  gages — Explanation  of  the  popularity  of  common  calipers 
— Limit  gages — Improved  construction  of  snap  gages — Causes  which 
restrict  the  use  of  gages — The  Johansson  combination  gages,  their 
principles  and  properties — Uses  of  these  gages — Screw  thread  gages — 
Independent  measurements  of  the  various  elements  of  screw  threads— 
Measuring  the  errors  of  pitch  of  long  screws. 

THE  FUNCTION  OF  STIFFNESS  IN  GAGES 

Referring  again  to  the  Brown  and  Sharpe  plugs,  Fig.  52,  an 
important  lesson  may  be  learned  by  comparing  them  by  means 
of  a  pair  of  common  calipers.  Using  the  gage  shown  with  them 
the  difference  between  them  may  be  detected  by  any  one,  but 
using  common  calipers,  an  unskilled  person  will  find  this  detec- 
tion impossible.  Using  calipers  a  tool  maker  would  detect  the 
difference  with  reasonable  certainty  but  the  fact  remains  that 
while  with  the  gage  this  detection  is  easy,  with  the  calipers  it  is 
difficult. 

This  difference  between  the  two  instruments  is  due  to  the 
increased  stiffness  of  the  snap  gage  as  compared  with  the 
calipers.  It  is  clear  that  when  either  gage  or  calipers  is  passed 
over  the  larger  plug  the  instrument  must  spring  to  accommodate 
the  increased  size.  Because  of  the  stiffness  of  the  snap  gage, 
the  increased  effort  required  to  push  it  over  the  larger  plug  is 
sufficient  to  be  felt  by  the  hand  while,  because  of  the  flexi- 
bility of  the  calipers,  this  increased  effort  is  so  small  that,  to  all 
but  the  highly  skilled,  it  is  imperceptible.  This  shows  at  once 
the  function  of  stiffness  in  gages  which  become  more  sensitive 
as  they  are  made  stiffer  with,  however,  a  limitation  which 
grows  out  of  the  fact  that  increased  stiffness  is  necessarily 
accompanied  by  increased  weight  and  this  increased  weight,  if 

111 


112 


METHODS  OF  MACHINE  SHOP  WORK 


GAGES  113 

carried  too  far,  dulls  the  sense  of  touch.  Were  the  snap  gage 
of  Fig.  52  to  weigh  ten  pounds,  for  example,  the  increased 
effort  necessary  to  force  it  over  the  larger  plug  would  be  lost 
in  the  weight  of  the  gage  and  the  hand  would  not  feel  it. 

This  consideration  has  immediate  application  to  large  gages. 
Were  the  weights  of  large  gages  made  proportional  to  their  sizes 
in  order  to  maintain  the  stiffness,  the  effect  would  be  to  destroy 
the  very  object  of  this  construction  by  reason  of  its  effect  in 
dulling  the  sense  of  touch  and,  moreover,  such  gages  would  be 
clumsy  and  unwieldy.  It  is,  consequently,  impracticable  to 
make  large  gages  of  the  same  relative  stiffness  as  small  ones  and 
this  compels  us,  when  using  large  gages,  to  resort  to  expedients. 
Because  of  their  comparative  flexibility  large  gages  are  subject 
to  distortion  from  the  effect  of  their  own  weight  and,  if  satis- 
factory measurements  are  to  be  obtained,  it  is  necessary  to  find 
means  by  which  this  distortion  may  be  neutralized. 

Figs.  93  and  94  show  such  an  expedient  used  at  the  works  of 
the  Westinghouse  Machine  Company.  The  piece  of  work  to 
be  gaged — shown  beyond  the  operator  and  in  the  lathe — is  a 
thirty-nine  inch  crank  shaft,  in  front  of  which  is  a  micrometer 
caliper  of  suitable  size.  In  order  to  combine  lightness  with 
stiffness  as  far  as  possible,  the  frame  of  the  caliper  is  made  of 
aluminum  alloy.  At  its  upper  end  it  carries  a  micrometer 
head  which  has  a  range  of  adjustment  of  one  inch.  At  its 
lower  end  is  an  adjustable  anvil  screw  having  a  range  of  sev- 
eral inches  in  order  to  give  the  instrument  a  corresponding 
range  and  thus  reduce  the  number  of  instruments  required  for 
a  given  total  range. 

Fig.  93  shows  the  instrument  in  process  of  adjustment.  Sup- 
ported by  a  suitable  stand  is  an  end  measure  rod  of  steel  which 
is  protected  from  the  temperature  of  the  hand  by  a  casing  of 
wood.  This  rod  is  of  a  length  equal  to  the  number  of  whole 
inches  desired — the  fraction  being  obtained  from  the  micro- 
meter head.  At  the  lower  end  of  the  supporting  stand  is  a 
stirrup  supported  in  springs  of  a  strength  sufficient  to  carry 
the  weight  of  the  micrometer.  When  adjusting  the  instru- 
ment the  micrometer  head  is  first  set  to  zero  and  then,  with  the 
instrument  resting  in  the  stirrup  in  the  position  of  Fig.  93,  the 


114  METHODS  OF  MACHINE  SHOP  WORK 

anvil  screw  is  adjusted  until  the  micrometer  screw  makes  con- 
tact with  the  top  of  the  rod.  The  fractional  part  of  an  inch 
desired,  if  any,  is  then  obtained  by  turning  back  the  micro- 
meter when  the  adjustment  is  complete. 

When  gaging  the  shaft  two  light  sling  chains  are  passed 
around  it  as  shown  in  Fig.  94,  which  chains  carry  a  spring  sup- 
ported stirrup  identical  with  the  one  on  the  stand  for  the  end 
measure  rod.  The  caliper  is  placed  in  the  stirrup  and  the  size 
of  the  shaft  is  read  from  the  micrometer.  The  object  of  the 
whole  arrangement  will  be  seen  to  be  to  place  the  instrument  in 
the  same  position  as  regards  gravity  when  adjusting  it  and 
when  measuring  with  it,  by  which  expedient  the  deflection  due 
to  its  own  weight  is  obviously  nullified. 

GAGES  CONTRASTED  WITH  CALIPERS 

Snap  gages  have  the  defects  of  their  virtues.  The  stiffness 
which  gives  rise  to  their  extreme  sensitiveness  gives  rise  also  to  a 
property  which  makes  them,  for  many  purposes,  an  unsatisfac- 
tory substitute  for  spring  calipers.  Because  of  their  flexibil- 
ity, the  calipers  may  be  pushed  over  a  piece  of  work  before  it 
has  reached  the  final  size  without  disturbing  the  adjustment  or 
doing  other  damage  and  the  skill  of  the  workman  connects  the 
pressure  required  to  push  the  calipers  over  the  work  with  the 
amount  of  metal  remaining  to  come  off.  This  is  an  extremely 
valuable  property  of  the  calipers.  Because  of  its  stiffness,  the 
snap  gage  cannot  be  pushed  over  the  work  until  the  work  has 
reached  size.  If  it  does  not  go  over,  it  tells  the  workman  that 
there  is  more  metal  to  come  off  but  it  gives  no  indication  of  how 
much  more,  the  result  being  an  increased  number  of  trial  cuts. 

By  reason  of  their  flexibility  the  calipers  may  be  used  for 
work  of  various  degrees  of  accuracy.  For  close  work  the  size 
is  made  such  that  the  feel  of  the  contact  between  calipers  and 
work  is  very  light,  while  for  coarser  work  the  contact  is  heavier — 
the  calipers  going  over  the  work  in  both  cases.  The  stiff  snap 
gage  will  not  go  over  the  work  at  all  until — within  very  narrow 
limits — the  work  is  as  small  as  true  gage  size.  To  tell  the 
workman  to  work  to  the  gage  means,  therefore,  that  in  many 


GAGES  115 

cases  he  will  make  fits  that  are  unnecessarily  good  and  hence 
unnecessarily  expensive.  On  the  other  hand,  to  depart  from 
this  by  authorizing  him  to  use  his  judgment  regarding  the  de- 
gree of  correspondence  between  gage  and  work,  is  to  lose  that 
very  control  of  the  sizes  for  which  the  gage  system  is  adopted 
and  so  practically  abandon  the  system  at  the  outset. 

All  this  is  epitomized  in  the  expression  that  "gages  give  no 
warning"  as  the  desired  size  is  approached,  and,  since  they  give 
none,  the  size  must  be  approached  with  extreme  care  and  in 
constant  fear  that  a  cut  may  be  too  heavy  and  so  spoil  the  work. 
For  these  reasons  calipers  hold,  and  always  will  hold,  their 
own  for  many  kinds  of  work,  especially  those  in  which  the  work- 
man adjusts  the  tool  for  each  piece  produced,  ordinary  lathe 
work  being  a  typical  example. 

LIMIT  GAGES 

These  facts,  combined  with  a  recognition  of  the  further  fact 
that  exact  duplication  of  sizes  is  an  impossibility,  has  led  to  the 
system  of  limit  gages  of  which  three  forms  are  shown  in  Figs. 
95-97. 1  Of  these  Figs.  95  and  96  are  external  and  Fig.  97 
internal  gages.  In  all  cases  one  end  is  larger  than  the  other 
by  a  predetermined  amount  as  indicated  by  the  figures  stamped 
on  Figs.  96  and  97.  In  the  use  of  these  gages  one  end  must  go 
over  or  within  the  work,  as  the  case  may  be,  and  the  other  must 
refuse  to  go  over  or  within  it.  The  work  is  thus  always  between 
the  sizes  of  the  two  ends  and,  by  a  proper  determination  of  the 
difference  between  the  ends,  any  required  grade  of  workmanship 
may  be  established. 

It  is  obvious  that  in  use  these  gages,  like  all  end  measures,  are 
subject  to  wear  and  it  is  also  obvious  that  this  wear  is  confined 
chiefly  to  the  end  that  goes  over  or  within  the  work.  Conse- 
quently it  is  customary,  especially  in  the  case  of  internal  gages, 
to  make  the  end  which  enters  the  longer  of  the  two,  thus  pro- 
viding increased  wearing  surface  and  also  showing  at  a  glance 
which  is  which.  For  purposes  of  distinction  the  two  ends  are 

1  Limit  gages  were  first  advertised  foi  sale  by  the  Brown  and  Sharpe  Manu- 
facturing Company  in  1875,  after  about  ten  years  prior  use  in  their  own  works. 


116 


METHODS  OF  MACHINE  SHOP  WORK 


distinguished  as  maximum  or  minimum  and  as  go  or  not-go. 
The  terms  maximum  and  minimum  are  not  satisfactory  because 
the  maximum  external  gage  goes  over  the  work  while  the  maxi- 
mum internal  gage  does  not  go  in.  The  terms  go  gage  and  not- 
go  gage  avoid  this  ambiguity  and  are  to  be  preferred. 


FIG.  95. 


.249 


ISZ'l 


FIG.  96. 


FIG.  97. 


Limit  gages. 


Fig.  98  shows  a  modification  of  the  snap  gage  designed  to  avoid 
the  necessity  for  renewal  after  wear  has  taken  place.  This 
effect  is  accomplished  by  the  combination  of  the  center  piece  a 
and  measuring  jaws  b.  The  original  size  of  the  gage  is  deter- 


GAGES 


117 


mined  by  the  center  piece  while  the  effect  of  wear  is  confined 
to  the  jaws.  After  the  jaws  have  worn  it  is  only  necessary  to 
remove  them,  lap  them  flat  again  and  then  replace  them  in 
order  to  restore  the  gage  to  its  original  size  and  with  a  trifling 
degree  of  expense.  This  construction  will  be  recognized  as 


FIG. 


FIG.  99. 
Modified  snap  and  limit  gages. 


FIG.  100. 


another  application  of  the  principle  of  the  division  of  functions 

When  limit  gages  are  made  upon  this  plan  it  is  necessary 

that  the  limit  be  ground  into  the  center  piece  as  in  Fig.  100  and 

not  into  the  jaws  as  in  Fig.  99.     If  the  limit  is  ground  into  the 


FIG.  101. — A  collection  of  limit  gages. 

jaws  it  must  be  repeated  every  time  the  jaws  are  lapped 
whereas,  if  ground  into  the  center  piece,  the  lapping  becomes, 
as  with  the  single  gage,  a  simple  process  of  restraightening  the 
jaws.  In  some  cases  the  go  and  not-go  gages  when  made  on 
this  plan  are  entirely  separate  and  then  bolted  together,  forming 


118  METHODS  OF  MACHINE  SHOP  WORK 

two  gages  in  fact,  though  one  as  a  matter  of  convenience. 
Fig.  101  shows  a  collection  of  such  gages  at  the  works  of  the 
Hess-Bright  Manufacturing  Company,  who  have  many  hundred 
such  gages  in  use. 

THE  COST  OF  GAGES  AND  SUBSTITUTES  FOR  THEM 

The  use  of  limit  gages  is  restricted  by  their  high  cost  and 
their  inflexibility  as  regards  the  limits.  One  may  have  two 
pieces  of  work  of  the  same  nominal  size  in  one  of  which  the  limits 
may  be  wider  than  the  other  and,  if  advantage  is  to  be  taken  of 
this,  two  sets  of  limit  gages  must  be  provided.  The  gages  should 
always  be  in  duplicate — a  working  set  and  an  inspector's  set — 
and  in  addition  to  this  there  should,  by  rights,  be  a  third  or 
reference  set  used  for  nothing  except  to  check  the  wear  on  the 
other  sets.  With  a  pair  of  limit  gages  once  made  the  limits 
are  fixed  and  unchangeable.  After  limits  have  been  set  one 
sometimes  finds  it  desirable  or  necessary  to  change  them,  in 
which  case,  with  the  gage  described,  there  is  nothing  to  do  but 
discard  the  old  and  install  new  ones.  The  effect  of  wear  also 
is  ever  present. 

These  considerations  indicate  the  large  investment  involved— 
an  investment  which  restricts  the  use  of  limit  gages  for  within 
what  their  merits  would  justify,  could  those  merits  be  considered 
independently  of  cost.  Because  of  the  cost  of  gages  the  micro- 
meter caliper  is  frequently  used  in  connection  with  the  limit  sys- 
tem. The  indicating  beam  caliper,  Figs.  70  and  71,  is  better 
adapted  to  this  purpose  than  the  micrometer  and  is,  in  fact,  an 
almost  ideal  instrument  for  the  great  number  of  cases  for  which 
the  cost  of  gages  prevents  their  use.  For  some  reason  which 
to  the  author  is  a  mystery,  it  has  never  received  a  tithe  of  the 
recognition  that  its  merits  deserve. 

ADJUSTABLE  LIMIT  GAGES 

Many  attempts  have  been  made  to  reduce  the  investment 
which  fixed  limit  gages  involve  by  making  them  adjustable 
through  a  considerable  range,  thereby  making  the  same  gage 
adaptable  to  pieces  of  different  sizes  and  to  those  of  the  same 


GAGES 


119 


nominal  size  but  with  different  limits  and  also,  incidentally, 
neutralizing  the  effect  of  wear. 

The  two  most  noteworthy  results  of  these  efforts  are  shown 
in  Figs.  102  and  104.  Fig.  102  shows  the  gage  of  the  (British) 
Newall  Engineering  Company.  The  go  and  not-go  fingers  are 
here  arranged  in  the  same  gap,  as  is  not  unusual  with  other 
constructions,  the  outer  ones,  of  course,  being  the  go  and  the 
inner  ones  the  not-go  fingers.  The  fingers  at  the  left  are  fixed 
but  those  at  the  right  are  adjustable,  the  range  of  adjustment 
in  the  gage  shown  being  from  three  to  three  and  one-half  inches. 
This  adjustment  is  used  to  vary  the  size  of  the  gage  within 


FIG.  102. — Newall  limit  gage. 


FIG.  103. — Adjusting  dial  and 
zero  of  the  Newall  gage. 


this  range  and  also  to  make  the  limits  closer  or  wider  according 
to  requirements.  With  these  gages  there  goes  a  set  of  fixed 
reference  standards — such  for  example  as  the  Brown  and  Sharpe 
reference  discs  already  shown  in  Fig.  51 — which  are  of  true  sizes 
without  reference  to  limits.  In  use,  both  fingers  of  the  gage 
shown  in  Fig.  102  are  first  adjusted  to  contact  with  the  reference 
gage  which  is  then  removed  and  a  graduated  dial  and  zero 
piece  are  placed  in  position  on  the  adjustable  measuring  fingers 
as  shown  in  Figs.  102  and  103  but  most  clearly  in  the  latter. 
Using  the  graduated  dial,  the  outside  or  go  finger  is  then  adjusted 
by  the  number  of  thousandths  by  which  it  is  to  differ  from  the 


120 


METHODS  OF  MACHINE  SHOP  WORK 


true  size.  The  index  dial  and  zero  piece  are  then  inverted 
in  position  and  the  not-go  finger  is  adjusted  by  the  amount  by 
which  it  is  to  differ  from  the  true  size.  The  index  dial  and  zero 
piece  are  then  removed  and  the  gage  is  ready  for  use. 

The  large  reduction  of  investment  due  to  this  form  of  gage  is 
obvious.  Because  of  the  range  of  adjustment  the  same  gage 
may  be  used  for  a  variety  of  sizes  and  for  the  same  nominal  size 
but  with  different  limits.  The  working  gage  may  also  be  used  as 
the  inspection  gage  by  re-examining  its  setting;  while,  the  refer- 
ence gages  being  of  true  size  only  without  regard  to  limits,  their 
number  is  largely  reduced.  Finally,  the  gage  being  reset 

repeatedly  to  agree  with  the 
reference  gage,  which  is  used 
so  little  that  its  wear  may  be 
ignored,  the  effect  of  wear  is 
practically  eliminated  and 
the  gages  need  never  be  re- 
newed from  that  cause. 

The  second  method  of  ac- 
complishing this  result  is 
found  in  the  limit  gages  of  C. 
E.  Johansson  of  Elkistuna, 
Sweden,  shown  in  Fig.  104. 
As  in  the  Newall  gage  we 
have  here  go  and  not-go  fin- 
gers in  the  same  jaws.  The 

fingers  are,  however,  simple  cylindrical  plugs  adjusted  by 
suitable  screws  in  their  rear  which,  being  sunk  in  the  yoke, 
do  not  show  in  the  illustration.  Unlike  the  Newall  gage,  these 
screws  are  adjusting  screws  only  and  do  no  measuring,  the  ad- 
justment being  determined  by  means  of  Mr.  Johansson's  com- 
bination gages  shown  in  Fig.  105. 

THE  JOHANSSON  COMBINATION  GAGES 

These  combination  gages,  which  made  their  appearance  on  the 
American  market  in  1907,  represent  the  culmination  of  precision 
measurements.  They  have  taken  the  mechanical  world  almost 
by  storm,  while  their  method  of  production  is  a  mystery.  A 


FIG.  104. — Johansson  limit  gage. 


GAGES  121 

set  of  these  gages  was  sent  to  the  National  Physical  Laboratory 
of  Great  Britain  for  examination.  The  laboratory  reported  that 
of  the  entire  set  no  discoverable  error  could  be  found  in  any 
except  two,  the  error  of  these  two  being  a  hundred  thousandth  of 
an  inch.  More  recently  (1913)  Mr.  Johansson  has  brought  out 
a  series  of  gages  differing  by  the  hundred  thousandth  of  an  inch. 
In  view  of  what  he  had  previously  accomplished,  it  is  scarcely 
too  much  to  say  that  no  one  living  is  competent  to  dispute  his 
claim.  Referring  to  Fig.  105,  which  shows  a  set  of  gages  in  their 
case,  the  upper  row  contains  a  series  of  nine  gages  ranging  in  size 
from  .  i  +  T¥o IF TT  to  .  i  +  TTriTTnr  in-  the  increment  between  the 
sizes  being  TO~~U~~O~O  in.1  The  second  and  third  rows  contain  a  ser- 


FIG.  105. — Johansson  combination  gages. 

ies  of  forty-nine  gages  ranging  in  size  from  .  i  +  TTTOTT  to  .  i  + 
Tirlrir  in.  the  increment  between  the  sizes  being  roVir  in.  Next 
comes  a  series  of  nineteen  gages  ranging  from  .05  to  .95  in., 
the  increment  being  T|-Q  in.  Finally,  in  the  bottom  row  are  a 
series  of  four  gages  ranging  between  one  and  four  inches  by 
increments  of  one  inch. 

In  addition  to  their  remarkable  accuracy  these  gages  are  also 
noteworthy  because  of  the  system  incorporated  in  their  sizes. 
The  comparatively  limited  number  of  gages  shown  in  the  box  is 
capable  of  giving  all  possible  sizes  within  their  range  with  incre- 
ments of  the  ten  thousandth  of  an  inch,  the  total  number  of 

1  Other  sets  are  made  in  which  the  thinnest  gage  measures  .01  inch. 


122  METHODS  OF  MACHINE  SHOP  WORK 

sizes  obtainable  with  the  set  of  gages  being  not  less  than  a  hun- 
dred thousand  and,  moreover,  most  of  the  sizes  may  be  obtained 
by  several  combinations. 

The  scheme  of  sizes  and  the  method  of  combining  them  by 
which  this  remarkable  result  is  accomplished  are  best  explained 
by  examples  as  follows: 

Beginning  with  the  first  gages  of  series  Nos.  i  and  21  and 
substituting  the  others  of  series  No.  i  in  their  order  we  obtain, 
by  addition,  the  sizes: 

From  series  No.  i:    .  1001      .1002     .1003  j    etc.   |    .1009 
From  series  No.  2 :    .  101        . 101        . 101     \  up  to  f    .  101 


Sum  .2011      .2012      .2013  .2019 

The  second  gage  of  series  No.  2  is  then  substituted  for  the 
first  and  the  combinations  with  the  gage  of  series  No.  i  are 
repeated,  giving: 

From  series  No.  i:    .  i2          . 1001      .1002  f    etc.    j    .1009 
From  series  No.  2:    .  102       . 102       . 102    1  up  to  f    .  102 


Sum  .1020     .1021      .1022  .1029 

The  third  gage  of  series  No.  2  is  then  substituted  and  the 
process  repeated,  giving: 

From  series  No.  i:     .  i2          . 1001      .1002}  etc.    j    .1009 
From  series  No.  2:     .103       .103       .103   jup  toj     .103 


Sum  .2030     .2031      .2032  -2039 

This  process  may  obviously  be  repeated  until  the  first  inch  is 
exhausted  when,  by  adding  the  i  inch  gage,  the  process  may  be 
repeated  up  to  two  inches  and  so  on. 

The  series  obtainable  includes  binary  as  well  as  decimal 
sizes  and,  moreover,  binary  sizes  plus  or  minus  any  number  of 

1  The  first  inch  cannot,  in  the  nature  of  the  case,  run  down  to  zero,  the  smallest 
obtainable  size  being  that  of  the  smallest  gage.  All  other  inches  are  without 
gaps  in  the  complete  list  of  ten  thousand  sizes  per  inch. 

*>•  The  .1  inch  gage  comes  from  the  third  series. 


GAGES  123 

thousandths   or    ten    thousandths    that   may   be   required   in 
connection  with  the  limit  system.     Thus,  to  get  if  in.  we  add: 

From  series  No.  4    i . 
From  series  No.  3       . 5 
From  series  No.  2      .125 


Sum  1.625 

Similarly  to  get  if  ins.  we  add: 

From  series  No.  4    i . 
From  series  No.  3      .75 
From  series  No.  2      .125 


Sum  1-875 

To  get  if  +  TTJTO-  ins.  we  add: 

From  series  No.  4    i . 
From  series  No.  3       . 5 
From  series  No.  2      .127 

Sum  1.627 

and  to  get  if  —  ToVo  ins.  we  add: 

From  series  No.  4    i . 
From  series  No.  3      . 5 
From  series  No.  2      .123 


Sum  1-623 
Similarly  to  get  2yV  ins.  we  add; 

From  series  No.  4  i . 
From  series  No.  3      . 7 
From  series  No.  3      . 5 
From  series  No.  2      .137 
From  series  No.  i      .  1005 

Sum  2.4375 


124 


METHODS  OF  MACHINE  SHOP  WORK 


APPLICATIONS  OF  THE  JOHANSSON  GAGES 

The  method  of  using  the  gages  in  setting  the  adjustable  limit 
gage,  Fig.  104,  will  now  be  apparent.  It  is  only  necessary  to 
produce  the  necessary  size  by  a  suitable  combination  of  gages, 
insert  them  between  the  measuring  fingers  and  adjust  the  latter 
to  contact. 

The  setting  of  the  limit  gage  is,  however,  but  a  small  part  of 
the  useful  applications  of  these  combination  gages  which  are 
used  for  a  great  variety  of  tool-making  processes.  Fig.  106 
shows  an  application  to  the  making  of  two  holes  d  and  c  at  exact 
distances  apart  represented  by  the  gages  a  and  b  The  piece 
of  work  in  which  the  holes  are  to  appear  is  bolted  to  the  face 
plate  of  a  lathe  against  suitable  parallel  strips,  as  in  the  left-hand 


—  1  —  1  — 

©    a 

r& 

a 

d^J 

-*1            H>~ 

©     ©                       © 

Parallel 


FIG.  1 06. — Use  of  Johansson  gages  for  spacing  holes. 

illustration,  and  the  first  hole  is  bored.  Gage  block  combina- 
tions representing  the  vertical  and  horizontal  distances  between 
the  holes  are  then  made  up  and  inserted  between  the  piece  of 
work  and  the  parallels,  resulting,  obviously,  in  a  movement  of  the 
piece  of  work  on  the  face  plate  such  that  if  the  second  hole  be 
bored  the  spacing  between  the  holes  will  be  the  one  required 
to  a  high  degree  of  precision. 

Fig.  107  shows  a  frame  which  accompanies  the  gages  by  which 
they  may  be  assembled  in  any  convenient  number  and  thereby 
produce  standards  by  which  to  adjust  either  inside  or  outside 
calipers.  In  this  application  the  gages  take  the  place  of  the 
customary  graduated  scale,  giving  all  sizes  possible  with  the 
scale  but  with  a  far  higher  degree  of  accuracy.  At  the  same 
time  the  valuable  properties  of  the  calipers  already  noted  are 


GAGES 


125 


retained  and  the  workman's  justifiable  preference  for  them  is 
respected.  The  uses  of  the  gages  are,  in  fact,  almost  numberless. 
A  property  which  they  have  and  which  appears  to  most  people 
as  new  although,  in  point  of  fact,  surfaces  sufficiently  good  to 
show  this  property  equally  well  have  been  made  for  many 
years,  is  that  of  adhesion.  If  two  of  the  measuring  surfaces  be 
wrung  together  after  careful  wiping  to  remove  adhering  dust, 
they  will  adhere  to  one  another,  as  shown  in  Fig.  108,  and  with 
sufficient  firmness  to  be  handled  and  used  as  though  one  piece 


FIG.  107. — Use  of  Johansson  gages  for  setting  calipers. 

—a  property  which  is  extremely  valuable  in  the  every-day  use  of 
the  gages.  This  adhesion  is  not  to  be  confused  with  the  mom- 
entary adhesion  of  surface  plates  which  is  commonly  attributed 
to  the  pressure  of  the  atmosphere.  With  the  gages  the  adhesion 
is  indefinite  in  point  of  time  and,  in  fact,  increases  with  the  time 
they  are  allowed  to  remain  in  contact.  So  pronounced  is  this  that 
the  user  is  instructed  not  to  leave  the  gages  in  contact  indefi- 
nitely because  it  may  lead  to  the  ultimate  necessity  for  vio- 
lence in  order  to  separate  them.  The  adhesion  has  been  meas- 
ured in  a  testing  machine  without  waiting  for  the  increase 


126  METHODS  OF  MACHINE  SHOP  WORK 

described,  and  the  force  necessary  to  pull  the  pieces  apart,  figured 
against  the  area  of  their  surfaces,  has  been  found  to  run  as  high 
as  the  equivalent  of  eleven  atmospheres — figures  which  rule  out 
the  common  explanation  that  the  adhesion  is  due  to  atmos- 
pheric pressure.  The  only  remaining  explanation  seems  to  be 
that  it  is  due  to  molecular  attraction  which  is  given  an  oppor- 
tunity to  act  by  reason  of  the  superior  closeness  of  contact 
due  to  the  perfection  of  the  surfaces. 

In  addition  to  gages  of  the  types  described,  the  microm  eter 
caliper  and  the  multiplying-lever  caliper,  as  already  ex- 
plained, are  applicable  in  connection  with  the  limit  system. 


i 


FIG.  1 08. — Adhesion  of  Johansson  gages. 

Both  these  instruments  show  the  amount  of  metal  remaining 
to  come  off  an  unfinished  piece  and  thus  have  the  property  of 
giving  warning  in  common  with  common  calipers,  and  even 
more  effectively,  because  they  show  the  exact  amount  remain- 
ing which  calipers  do  not. 

SCREW-THREAD  GAGES 

An  important  application  of  the  gage  system  is  to  the  gaging 
of  screw  threads,  a  standard  type  of  screw-thread  gage  by  the 
Pratt  and  Whitney  Company  being  shown  in  Fig.  109.  The 
external  gage  is  adjustable  within  narrow  limits,  two  screws, 
one  of  which  is  a  pull  and  the  other  a  push  screw,  locking  the 
gage  in  position  and  providing  for  adjustment  both  to  compen- 
sate for  wear  and  to  provide  for  the  character  of  the  fit  between 


GAGES 


127 


a  screw  and  its  nut.  These  gages  are  in  large  use  for  the 
gaging  of  manufactured  products,  of  which  they  insure  inter- 
changeability,  but  for  some- 
classes  of  tool-room  work  some 
thing  more  is  needed  in  order 
to  measure  independently  the 
various  elements  of  a  screw. 

If   a  screw   enters    the  gage 
that  fact  shows  it  to  be  inter- 
changeable with   other  screws 
but  if  it  refuses  to  enter,  the  gage 

does  not  show  which  of  several  FlG-  109 —Plug  and  ring  screw  thread 

gages. 

elements  is  at  fault.     Thus  the 

screw  may  be  bodily  too  large  as  measured  on  the  inclined  sur- 


FIG.  no.  —  Micrometer  for  measuring  screw  threads. 

faces  which  are  the  surfaces  at  which  the  fit  should  be  made. 

On  the  other  hand,  the  screw  may  refuse 
to  enter  because  too  large  at  the  outer 
diameter  or  at  the  root  diameter,  neither 
of  which  is  of  importance  in  the  action 
of  the  screw.  Again  the  screw  may 
refuse  to  enter  because  the  pitch  is  too 
large  or  too  small  but,  among  these 
various  reasons  for  failure  to  enter,  the 
gage  makes  no  discrimination.  While 
satisfactory  as  a  go  gage,  this  construe- 
tion  is  therefore  inadequate  for  the 
detection  of  the  source  of  error  of  incor- 
rect screws,  and  for  this  reason  other 


of 

diameters. 


128 


METHODS  OF  MACHINE  SHOP  WORK 


Fie.  112. — Application  of  the  wire  method  to  the  gaging  of  worm    threads. 

methods  have  been  devised  by  which  to  measure  the  elements 
individually. 

The  most  important  elements 
are  the  diameter  as  measured  on 
the  inclined  surfaces  of  the  threads, 
because  these  are  the  surfaces  at 
which  the  fit  should  be  made,  and 
the  pitch.  A  very  common  method 
of  measuring  the  diameter  is  by 
the  Brown  and  Sharpe  screw- 
thread  micrometer  caliper  shown 
in  Fig.  no.  The  measuring  fin- 
gers of  this  instrument  are  ground 
to  the  angle  of  the  thread,  the  V's 
being  truncated  to  insure  they  do 
not  reach  the  bottom  of  the  thread 
and  that  they  make  contact  on  the 
thread  sides  only. 

Another  method  of  measuring 
the  thread  sides  is  shown  in  Fig. 
in,  in  which  wires  of  known  di- 


ameter  are  placed  in  the  threads 


FIG.    113. — Limit   gage   for   screw 
threads. 


GAGES 


129 


and  the  measurement  is  made  by  means  of  the  usual  mi- 
crometer over  the  outsides  of  the  wires.  Complete  tables 
of  readings  for  standard  threads  have  been  worked  out  for  this 
system,1  which  is  admirably  adapted  to  the  gaging  of  large 
screws  and  worms,  an  illustration  of  this  use  of  it  being  given 
in  Fig.  112  from  the  British  firm,  David  Brown  and  Sons.  In 
this  case  no  absolute  measurement  is  made,  the  worm  being 
compared  with  a  standard  by  means  of  the  apparatus  shown 
which,  after  what  has  been  said,  is  self-explanatory. 

Fig.  113  shows  the  limit  gage  system  applied  to  this  measure- 
ment, the  instrument  illustrated  being  by  the  Wells  Brothers 


FIG.  114. — Gage  for  the  pitch  of  screw  threads. 

Company.  As  in  the  case  of  other  limit  gages  shown,  the 
outer  fingers  are  of  the  go  and  the  inner  fingers  of  the  not-go 
dimensions.  For  the  gaging  of  the  pitch  the  instrument 
shown  in  Fig.  114,  also  by  the  Wells  Brothers  Company,  is 
very  satisfactory.  By  placing  a  gage  of  this  type  against  the 
threads  to  be  gaged,  very  minute  discrepancies  between  the 
thread  and  the  gage  are  apparent. 

Fig.  115  shows  another  instrument  by  which  errors  of  pitch 
are  not  only  shown  but  measured.  Two  stationary  measuring 
fingers  a  and  b  are  attached  to  the  frame  and  a  moving  finger 

1  These  tables  may  be  found  in  the  American  Machinists'  Handbook  by  F.  H. 
Colvin  and  F.  A.  Stanley. 
9 


130 


METHODS  OF  MACHINE  SHOP  WORK 


c  is  attached  to  a  sliding  bar  d.  The  moving  finger  abuts 
against  the  multiplying  lever  e  which  plays  over  a  graduated 
scale  at  its  top.  With  the  fingers  a,  c,  exactly  one  inch  or  the 
fingers  b,  c  exactly  one-half  inch  apart,  the  multiplying  lever 
reads  zero  and  by  inserting  the  screw  to  be  tested  as  shown  the 


FIG.  115. — Instrument  for  measuring  the  pitch  of  screw  threads. 


error  of  the  pitch  is  read  in  thousandths.  The  right-hand  meas- 
uring finger  is  supplied  in  order  to  measure  screws  of  less  than 
one  inch  length. 

All  these  devices  are  for  the  measurement  of  short  screws. 
An  equipment  for  measuring  the  errors  of  pitch  of  lead  screws, 


GAQES 


131 


from  the  works  of  the  Hendey  Machine  Company,  is  shown  in 
Fig.  116.  The  lead  screw  to  be  tested  passes  through  the 
hollow  spindle  and  is  gripped  in  a  chuck  by  which  it  may  be 
turned  by  a  covered  worm  gear  and  the  crank  at  the  left,  an 
index  wheel  and  stationary  zero  enabling  the  screw  to  be  turned 
an  exact  number  of  revolutions.  The  screw  traverses  a  carriage 
along  the  bed  of  the  machine.  Clamped  to  the  bed  in  the  rear 
of  the  carriage  is  a  block  carrying  a  micrometer  head.  Begin- 
ning with  the  micrometer  head  finger  in  contact  with  a  second 


FIG.  1 1 6. — Measuring  errors  of  pitch  of  lead  screws. 


finger  on  the  carriage,  the  screw  is  given  such  a  number  of  turns 
as  would,  were  the  screw  without  error,  advance  the  carriage 
an  exact  inch.  This  being  done,  a  one-inch  end-measure  rod 
is  placed  between  the  finger  points  on  the  carnage  and  the 
micrometer,  when  the  error  of  the  movement  for  that  inch  of 
traverse  is  read  off.  Turning  the  screw  so  as  to  advance  the 
carriage  another  inch,  the  reading  of  the  micrometer  is  again 
taken  with  a  two-inch  end-measure  rod  and,  in  this  way,  the 
errors  of  the  screw  may  be  determined  and  mapped. 


132 


METHODS  OF  MACHINE  SHOP  WORK 


THE  STAR  GAGE 

For  the  measurement  of  long  holes,  especially  those  of  the 
tubes  and  hoops  of  artillery,  the  gages  described  are  not  appli- 
cable and  a  special  construction,  the  star  gage,  Figs.  117-120,  is 
used.  This  gage  is  made  both  as  a  micrometer  and  as  a 
vernier  instrument,  the  former  being  shown  in  elevation  and 
section  in  Fig.  117  and  the  latter  in  use  in  Figs.  118-120.  The 
construction  is  the  same  in  both  forms  except  as  relates  to  the 
method  of  reading  the  indications.  Referring  to  Fig.  117  the 


FIG.  117. — Construction  of  the  star  gage. 


measuring  fingers  will  be  seen  to  be  pushed  inward  by  springs 
and  to  abut,  by  their  conical  ends,  against  the  similar  conical 
end  of  a  central  push  rod.  At  the  right-hand  end  is  a  microm- 
eter barrel,  similar  to  those  of  ordinary  micrometer  calipers, 
which  actuates  the  central  push  rod  and  by  which  variations  of 
the  work  from  a  standard  are  determined.  In  order  to  ac- 
commodate work  of  varying  length  the  central  push  rod  and  the 
surrounding  tube  are  provided  in  various  lengths  suitable  to  the 
work. 

Figs.  118  and  119,  from  the  Bethlehem  Steel  Company, 
show  the  measuring  fingers  in  the  act  of  gaging  a  gun  tube,  the 
measurement  in  the  former  case  being  that  of  a  tube  before  the 
rifling  has  been  done,  while  in  the  latter  the  tube  has  been  rifled, 
the  measuring  fingers  being  of  a  form  to  span  the  grooves. 
Fig.  120  shows  the  reading  end  of  the  gage  at  the  breech  end  of 
the  gun.  The  central  push  rod  is  slid  endwise  in  its  tube  by  the 
hand  lever  shown  until  the  measuring  fingers  make  contact 


GAGES 


133 


FIGS.  118  and  119. — The  star  gage  in  use. 


134 


METHODS  OF  MACHINE  SHOP  WORK 


with  the  bore.  At  the  left  of  the  lever  an  opening  is  cut  through 
the  tube  disclosing  the  graduations  on  the  push  rod  against 
which,  and  attached  to  the  tube,  is  the  vernier. 


FIG.  120. — Reading  end  of  star  gage  in  use. 


CHAPTER  VI 
FITS  AND  LIMITS 

The  limit  system  of  manufacture — Definition  of  terms — The  shaft  and 
the  hole  bases  for  fits — Differences  between  American  and  British  practice 
— Influence  of  the  grinding  machine — Examples  of  tolerances  in  various 
work— Taper  fits. 

THE  LIMIT  SYSTEM  OF  MANUFACTURE 

The  expressions  limit  and  limit  system  have  been  freely 
used  and  it  becomes  necessary  to  say  more  about  the  system 
as  distinguished  from  the  gages  which  go  with  it. 

The  limit  system  is  not  to  be  looked  upon  as  a  letting  down 
of  the  bars  as  regards  workmanship  but  rather  as  a  recognition 
and  control  of  the  inevitable.  The  makers  of  standard  gages 
do  not  claim  their  instruments  to  be  of  exact  sizes,  the  usual 
guarantee  being  that  they  are  correct  within  the  forty-thou- 
sandth of  an  inch,  that  is,  they  may  be  a  forty-thousandth  too 
large  or  the  same  amount  too  small.  If  gages  are  not  made  to 
absolute  sizes  much  less  is  any  other  class  of  work  so  made. 
Stove  lids  have  already  been  mentioned  as  work  which  is  inter- 
changeable without  being  accurate,  and  the  essential  difference 
between  stove  lids  and  gages  is  that  the  former  are  made  be- 
tween wide  and  the  latter  between  narrow  limits.  It  is  simply 
a  matter  of  determining  what  the  limits  shall  be  in  order  to 
establish  any  grade  of  workmanship  desired  between  that  of 
stove  lids  and  of  gages.  Whatever  the  class  of  work,  some 
variation  in  the  size  of  parts  which  are  nominally  alike  is  inev- 
itable and  the  limit  system  simply  sets  meets  and  bounds  to 
this  variation. 

The  statement,  which  one  often  hears,  that  a  piece  of  work 
is  exactly  right  means  no  more  than  that,  with  the  measuring 
instruments  at  hand,  its  errors  are  not  discoverable.  If  parts 
are  made  to  a  boxwood  rule  it  is  easy  to  so  make  them  that, 
with  that  instrument,  no  errors  can  be  discovered  although,  if 

135 


136  METHODS  OF  MACHINE  SHOP  WORK 

measured  with  a  micrometer,  errors  will  at  once  appear.  Simi- 
larly, parts  may  be  made  to  a  micrometer  which,  measured 
with  that  instrument,  will  show  no  error  although,  if  measured 
with  a  measuring  machine,  they  will  be  found  to  contain  errors. 
Accuracy  is  a  matter  of  degree  only,  absolute  accuracy  being 
unobtainable. 

DEFINITION  OF  TERMS 

In  connection  with  the  limit  system  three  terms  are  used 
which,  while  not  always  properly  used,  should  be  defined. 

An  engine  shaft  must  turn  in  its  bearings  and,  in  order  that 
it  may  do  so,  the  shaft  must  be  smaller  than  the  bearing  by  an 
amount  suitable  for  lubrication.  Similarly,  if  the  shaft  is  to  be 
forced  into  its  crank,  the  diameter  of  the  shaft  must  be  larger 
than  the  bore  of  the  crank  in  order  that  the  parts  may  be  securely 
fastened  together.  In  both  cases  the  parts  must  differ  from 
each  other,  and  this  difference  between  the  sizes  of  the  two  mat- 
ing pieces  due  to  the  character  of  the  fit  is  called  the  allowance. 

As  will  be  explained  more  fully  presently,  the  allowance  may 
be  placed  on  either  piece,  but,  assuming  for  the  moment  that 
the  intended  size  of  the  hole  is  the  nominal  size,  the  allowance 
for  the  shaft  is  added  to  the  nominal  diameter  for  a  press  fit 
and  subtracted  from  it  for  a  running  fit.  The  allowance  being 
thus  added  to  or  subtracted  from  the  nominal  size,  the  result 
is  the  intended  size  of  the  shaft.  From  the  intended  size  the 
actual  size  of  each  piece,  when  made,  will  differ,  because  of  the 
fact  that  the  exact  production  of  any  intended  size  is  an  impos- 
sibility. Moreover,  not  only  will  the  pieces  differ  from  the 
intended  sizes  but  they  will  differ  among  themselves  and,  recog- 
nizing that  some  variation  is  inevitable,  it  becomes  necessary 
to  decide  how  much  variation  is  permissible,  this  variation 
being  small  in  high-class  work  and  larger  in  more  common  work. 
The  variation  between  the  largest  and  smallest  sizes  which  is 
thus  decided  upon  as  permissible  is  called  the  tolerance. 

The  allowance  is  an  intentional  difference  between  the  sizes  of 
the  two  mating  pieces,  while  the  tolerance  is  an  unavoidable 
variation  from  the  intended  size.  The  allowance  applies  to 
one  piece,  the  tolerance  to  both. 


FITS  AND  LIMITS  137 

Finally  the  two  extreme  sizes  are  the  limits,  the  tolerance 
being  the  difference  between  the  high  and  the  low  limits.  The 
actual  sizes  as  made  may  fall  anywhere  between  the  limits. 

Of  the  above  terms,  allowance  is  very  commonly  used  as 
defined.  The  words  tolerance  and  limit  are,  however,  used 
somewhat  loosely  and  even  interchangeably.  One  will  often 
hear  the  expression  that  the  limit  on  a  certain  piece  is  one  or 
more  thousandths,  the  meaning  being  that  the  tolerance  is  one 
or  more  thousandths.  This  usage,  however,  is  not  often  the 
cause  of  confusion. 

VARIATIONS  IN  PRACTICE 

In  some  cases  the  tolerance  is  all  placed  on  one  side  of  the 
intended  size,  the  intended  size  being  one  of  the  limits — a 
practice  that  is  illustrated  in  the  diagrams,  Figs.  121  and  122. 
In  other,  and  probably  more  numerous,  cases,  the  limits  are 
placed  each  side  the  intended  size,  the  variation  from  the 
intended  size  being  one-half  the  total  variation  between  the 
largest  and  the  smallest  pieces.  When  this  practice  is  followed 
the  variation  from  the  intended  size  is  sometimes  called  the 
tolerance  although  but  one-half  the  total  range  which  is  toler- 
ated. It  is  from  this  that  the  usage  of  the  word  tolerance  was 
derived,  and  the  use  of  the  word  for  the  total  variation  between 
the  largest  and  smallest  sizes  tolerated  seems  to  the  author  the 
more  logical.  For  this  reason  the  word  has  been  thus  used 
throughout  the  accompanying  text. 

These  considerations  point  out  a  serious  limitation  of  any 
system  of  gages  which  give  the  true  sizes  only.  Whether  we 
have  to  deal  with  a  running  or  a  press  fit,  four  sizes  must  be 
considered — the  two  limits  of  the  shaft  and  the  two  of  the  hole. 
Of  these  four  sizes  such  a  system  of  gages  can  give  but  one,  the 
allowance  remaining  a  matter  of  judgment  and  skill  as  when 
graduated  scales  are  used,  while  no  provision  for  the  tolerance 
of  either  piece  is  made. 

THE  SHAFT  AND  THE  HOLE  BASES  OF  FITS 

Since  in  both  running  and  press  fits  the  intended  size  of 
either  part  may  be  equal  to  the  nominal  size  while  the  intended 


138  METHODS  OF  MACHINE  SHOP  WORK 

size  of  the  other  must  differ  from  the  nominal,  there  is  liberty 
of  choice  between  the  pieces  as  relates  to  the  one  of  which  the 
intended  size  shall  be  the  true  size  and  to  the  one  on  which  the 
allowance  shall  be  placed,  it  being  understood  that  the  one  of 
which  the  intended  size  is  the  true  size  is  still  made  between 
limits,  which  is  to  say  that  while  it  does  not  have  allowance 
it  does  have  tolerance. ' 

Growing  out  of  this  liberty  of  choice,  two  systems  of  con- 
struction are  in  use.  In  the  first,  called  the  hole  basis,  the 
hole  is  made,  within  limits,  of  the  true  size,  the  allowance  being 
placed  on  the  shaft,  while  in  the  second,  called  the  shaft 
basis,  the  shaft  is  made,  within  limits,  of  the  true  size  and  the 
allowance  is  placed  on  the  hole.  In  work  of  which  the  sizes 
of  both  pieces  are  determined  by  the  adjustment  of  the  tool,  as 
in  engine-lathe  or  boring-mill  work,  there  is  little  choice  between 
the  systems,  but  in  work  made  with  tools  which  are  set  to  a 
given  size  which  is  repeated  indefinitely  in  the  work,  there  is  a 
large  advantage  in  keeping  the  hole  as  nearly  as  possible  to  the 
true  size  and  throwing  the  allowance  on  the  shaft.  This  is  due 
to  the  fact  that  in  work  of  this  character  the  holes  are  commonly 
finished  with  reamers  and,  by  adopting  this  practice,  the  same 
reamer  may  be  used  for  all  classes  of  fits  of  the  same  nominal 
size,  the  shaft  being  made  slightly  smaller  for  a  running  and 
slightly  larger  for  a  press  or  shrink  fit.  Meanwhile,  since  this 
practice  is  most  desirable  for  work  of  this  character,  it  is  natural 
and  desirable  for  the  sake  of  uniformity  to  adopt  it  for  all  kinds 
of  work. 

In  this  respect  there  is  a  difference  of  practice  between  Ameri- 
can and  British  work.  In  the  United  States  the  hole  is  com- 
monly, though  not  universally,  kept  as  nearly  as  possible  to  the 
true  size,  while  in  Great  Britain  the  opposite  practice  prevails.1 

These  terms  are  illustrated  diagrammatically  and  grossly 
exaggerated  in  Figs.  121  and  122  for  both  hole  and  shaft  bases, 
the  allowances  and  tolerances  being  divided  by  two  because 
in  the  diagram  we  deal  with  radii  while  the  measurements  are 

1  This  statement  regarding  the  practice  in  Great  Britain  is  based  on  the  author- 
ity of  the  report  of  the  British  Engineering  Standards  Committee,  rendered  in 
1906. 


FITS  AND  LIMITS 


139 


made  across  the  diameters.  The  same  terms  apply  to  press  fits, 
understanding  that  in  such  fits  the  shaft  is  larger  than  the  hole 
instead  of  smaller  as  in  running  fits. 

In  this  as  in  many  other  matters  the  growing  use  of  the  grind- 
ing machine  has  had  large  influence,  especially  in  reducing  the 
tolerance  on  the  shafts.  With  the  holes  made  with  reamers  and 
the  shafts  in  an  engine  lathe  it  is  easier  to  keep  down  the  toler- 
ance on  the  holes  than  on  the  shafts  and,  consequently,  in  work 


In  tended.  Size  and 
{L'ower  Limit  of 
Bearing 


'rL'imit 
of  Bearing 


n  tended  Size.  True 

ze  and  Lower 
'L  imit  of  Bearing 


FIG.  121. — Hole  basis.  FIG.  122. — Shaft  basis. 

Allowances,  tolerances  and  limits. 

so  made,  the  tolerance  on  the  shafts  is  commonly  larger  than 
on  the  holes.  With  the  grinding  machine,  however,  the  reverse 
is  true  and  this  machine  has  thus  brought  about  an  improve- 
ment not  only  in  the  character  of  the  surfaces  as  respects  their 
roundness  and  straightness  but  also  in  their  sizes  as  respects 
the  tolerance. 

THE  VALUE  OF  THE  TOLERANCE  IN  PRACTICE 

In  an  actual  case  the  decision  regarding  the  allowance  and 
tolerance  is  a  matter  of  large  importance  and,  as  regards  lathe 


140 


METHODS  OF  MACHINE  SHOP  WORK 


work,  the  practice  of  several  leading  constructors  is  available 
for  general  use.  An  exhaustive  investigation  of  the  practice 
in  Great  Britain  as  relates  to  running  fits  was  made  by  the 
Engineering  Standards  Committee,  the  result  being  a  chart  in 
which  are  given  recommended  allowances  and  tolerances  for 
running  fits  of  three  grades  of  workmanship  and  for  shafts  up 
to  twelve  inches  in  diameter.  The  practice  of  the  General 
Electric  Company  for  sliding,  press  and  shrink  fits,  and  of  the 
Brown  and  Sharpe  Manufacturing  Company  in  allowances 
and  tolerances  for  ground  fits,  may  be  found  in  the  Transac- 
tions of  the  American  Society  of  Mechanical  Engineers,  Vols. 
24  and  32.  The  practice  of  the  C.  W.  Hunt  Company  for  all 
classes  of  fits  was  published  in  the  American  Machinist  for 
July  16,  1903,  and  of  the  Lane  and  Bidley  Company  for  press 
fits  in  the  same  periodical  for  July  30,  1899. 1 

It  is  neither  feasible  nor  necessary  to  give  all  these  data  here 
but  some  idea  of  the  magnitude  of  these  variations  should  be 
given,  if  only  to  correct  the  impression  among  beginners  that 
they  are  smaller  than  is  the  case.  The  accompanying  table 
gives  representative  values  of  tolerances  for  running  fits  from 
the  report  of  the  British  Engineering  Standards  Committee. 

BRITISH   STANDARD   TOLERANCES  FOR  THREE   GRADES   OF    RUNNING  FITS 


3  ir 

13 

is.  diam. 

6  ins.  diam. 

12  ins.  diam. 

13 

| 

1 

| 

13 

a 

13 

13 

cr 

cr 

cr 

cr 

cr 

cr 

cr 

cr 

cr 

H 

H 

no 

H 

-0 

<N 

nd 

en 

M 

"S 

"S 

Shaft  .... 

.0018 

•0035 

•0053 

.0025 

.005 

.0075 

.003 

.006 

.009 

Tolerance,  in. 

Hole  

.OOI7 

•0035 

.007 

.OO25 

.005 

.010 

.003 

.006 

.012 

Less  comprehensive  information  is  available  for  work  of 
other  character,  but  in  milling-machine  work  of  small  size  the 
tolerance  is  seldom  less  than  one-thousandth  of  an  inch,  two- 
thousandths  being  much  more  common,  the  tolerances  increasing 

1  These  and  other  data  relative  to  fits  have  been  collected  together  in  the 
author's  Handbook  for  Machine  Designers  and  Draftsmen. 


FITS  AND  LIMITS  141 

with  the  sizes  dealt  with  as  the  table  shows  them  to  do  in  the 
case  of  lathe  work. 

In  turret  lathe  work  of  moderate  size  the  tolerances  do  not 
differ  much*" from  those  of  milling-machine  work,  one-thousandth 
tolerance  being  feasible  for  pieces  which  do  not  exceed  about 
one  inch  in  diameter  when  such  workmanship  is  necessary,  but 
two- thousandths  being  much  more  common.  Such  a  reduction 
of  the  tolerance  is  always  accompanied  by  increased  cost. 
The  Cleveland  Automatic  Machine  Company  find  that  when  the 
tolerance  on  small  pieces  is  reduced  from  two-thousandths  to 
one,  the  output  of  their  automatic  turret  lathes  is  reduced  about 
twenty-five  per  cent.  This  loss  is  due  to  several  causes.  The 
cutting  tools  must  be  adjusted  more  carefully,  be  given  a  lighter 
cut  to  save  their  edges  and  be  ground  more  frequently. 

The  attempt  to  reduce  the  tolerance  below  about  one-thou- 
sandth increases  the  cost  at  a  rapidly  accelerated  rate,  a  point 
being  soon  reached  at  which  the  cost  is  prohibitive  and  another, 
not  far  from  it,  which  passes  the  ability  of  cutting  tools  and  the 
production  of  the  work  with  such  tools  becomes  mechanically 
impossible.  These  points  vary  with  the  size  of  the  work  and 
a  comprehensive  statement  regarding  them  is  a  difficult  one  to 
frame,  but,  for  work  not  exceeding  about  one  inch  diameter, 
a  single  thousandth  may  be  regarded  as  about  the  smallest 
feasible  tolerance  with  cutting  tools.  On  the  other  hand,  a 
good  grinding-machine  operator  will  maintain  sizes  within  a 
quarter  of  a  thousandth  without  difficulty. 

TAPER  PRESS  FITS 

The  most  approved  practice  with  press  fits  is  to  make  them 
taper,  the  taper  being  so  slight  as  not  to  endanger  the  security 
of  the  work  but  introducing  decided  advantages.  One  of  these 
advantages  is  that  the  two  pieces  may  be  compared  by  inserting 
the  plug  within  the  hole  when,  the  system  being  properly  laid 
out,  it  is  apparent  from  the  distance  by  which  the  plug  does  not 
go  home  if  the  parts  are  of  the  intended  sizes.  In  addition  to 
this  the  lubricant  is  not  scraped  off  as  in  the  straight  fit  method 
but  covers  the  entire  surface  when  the  pressing  action  begins. 
There  is  also,  partly  by  reason  of  this  and  partly  by  reason  of 


142 


METHODS  OF  MACHINE  SHOP  WORK 


the  fact  that  the  pressing  action  is  through  a  lesser  length,  much 
less  tendency  for  the  pieces  to  cut  and  score  one  another. 

The  customary  taper,  measured  on  the  diameters,  is  one- 
sixteenth  inch  per  foot  of  length.  This  taper  has,  however, 
been  improved  upon  by  the  Westinghouse  Machine  Company 
who  make  the  taper  .06  instead  of  .0625  =  one-sixteenth  inch 
per  foot.  This  modified  taper  is  equivalent  to  .005  inch  per  inch 
of  length  which  gives  even  thousandths  for  the  diameters  at 
each  inch  of  length.  The  Westinghouse  method  of  measuring 
these  tapers  is  shown,  with  the  taper  exaggerated,  in  Fig.  123. 


FIG.  123. — Measuring  taper  press  fits. 

A  strip  of  steel  having  holes  drilled  through  it  at  even  inches  of 
its  length  is  placed  within  the  hole  when,  by  the  inside  microm- 
eter caliper  shown,  the  hole  is  readily  gaged  at  any  part  of 
its  length.  The  readings  are  not  exactly  equal  to  the  diameters 
because  of  the  slight  inclination  of  the  caliper,  but  the  larger 
diameter  as  read  is  made  equal  to  the  diameter  called  for  in 
the  drawing,  the  difference  between  the  two  being  too  small  to 
be  of  any  importance. 


CHAPTER  VII 
DRIVING  SYSTEMS  FOR  MACHINE  TOOLS 

The  three  leading  systems  of  driving  and  their  proper  fields  of  use — 
Defects  of  the  old  type  of  cone  pulley  and  methods  of  overcoming  them — 
Individual  vs.  group  motor  driving. 

COMPARISON  OF  THE  CONE  PULLEY  AND  THE  VARIABLE  SPEED 
INDIVIDUAL  MOTOR  DRIVE 

Machine  tools  are  driven  by  the  following  methods: 

(a)  The  cone  pulley  and  back  gears,  power  being  obtained 
from  a  line  shaft. 

(b)  The  variable-speed  individual  electric  motor  and  back 
gears. 

(c)  The  constant-speed  pulley  and  a  set  of  gears  arranged  in 
a  gear  box  and  fitted  with  a  system  of  hand  levers  whereby  they 
are  quickly  shifted,  power  being  obtained  from  either  a  line  shaft 
or  a  constant-speed  individual  motor. 

The  variable-speed  motor  was  introduced  with  numerous 
claims  of  superiority  over  the  cone  pulley,  many  of  which  were 
imaginary,  but,  nevertheless,  when  contrasted  with  the  cone 
pulley  as  then  made,  it  was  found  to  have  advantages  which, 
while  not  inherent,  were  pronounced  and  they  gave  the  motor 
drive  a  great  vogue.  No  attempt  had  then  been  made  to 
develop  the  possibilities  of  the  cone  pulley.  To  shift  its  belt 
the  operator  had  to  get  a  pole,  which  might  or  might  not  be 
within  convenient  reach,  while  with  the  motor  there  was  sup- 
plied a  controller  at  the  operator's  elbow  by  which  the  speed 
changes  were  made  quickly  and  without  effort.  Consequently, 
while  with  the  cone  pulley  the  changes  were  often  neglected, 
with  the  motor  the  reverse  was  true,  the  result  being  an  in- 
creased output.  A  fundamentally  worse  defect  of  the  cone  pul- 
ley than  this  was  the  fact  that  the  intervals  between  successive 
speeds  were  much  too  large  while  the  intervals  between  the 
motor  speeds  were  much  smaller. 

143 


144  METHODS  OF  MACHINE  SHOP  WORK 

The  large  intervals  between  the  cone-pulley  speeds  led  to 
constant  loss  of  output.  It  is  not  a  matter  of  the  average  of 
gains  and  losses  but  of  average  losses.  The  cutting  speed  is 
limited  by  the  properties  of  the  cutting  tool  and,  except  in  the 
few  cases  when  the  cone  speed  is  equal  or  nearly  equal  to  the  cor- 
rect speed  for  the  work,  the  next  lower  cone  speed  must  always  be 
used,  the  result  being  in  nearly  all  cases  a  loss  from  the  possible 
output.  The  smaller  the  interval  between  the  speeds  the  smaller 
is  this  loss  and,  since  the  intervals  with  the  motor  were  smaller 
than  those  with  the  cone  pulley,  the  loss  was  smaller,  the  result 
being  another  increase  of  output.1 

Coincident  with  the  introduction  of  the  motor  drive  came  the 
introduction  of  high-speed  steel  and  the  great  movement  for 
intensive  production,  both  of  which  directed  attention  to  and 
served  to  emphasize  the  increased  output  which,  mistakenly, 
was  attributed  to  some  inherent  property  of  the  motor  drive. 

IMPROVED  PROPORTIONS  OF  THE  CONE  PULLEY 

There  is,  however,  another  serious  defect  of  the  cone  pulley  as 
commonly  and,  when  the  motor  drive  came  in,  universally  made 
which,  before  it  was  generally  understood,  acted  to  further  dis- 
credit the  cone-pulley  drive.  Because  of  defective  relative  pro- 
portions of  the  steps  the  belt  speed  was  unnecessarily  low  and 
the  driving  power  inadequate. 

As  the  belt  is  shifted  to  the  large  steps  of  the  driven  cone  its 
speed — never  very  high — is  seriously  reduced  until,  on  the  larger 
steps,  it  is  incapable  of  delivering  the  power  required  by  modern 
requirements  and  this  failure  is  just  at  the  point  where  power 
is  most  needed  by  reason  of  the  heavier  cuts  which  naturally  go 
with  large  work.  The  correction  of  this  deficiency  of  the  cone 
pulley  is,  however,  a  simple  matter  of  its  proportions. 

The  change  required  is  illustrated  in  Figs.  124  and  125,  the 
former  of  which  shows  the  older  defective  and  the  latter  the 
newer  improved  type.  The  change  consists  essentially  in 

1  The  ratio  between  successive  speeds  with  the  older  type  of  cone  pulley  is 
seldom  less  than  1.5.  It  frequently  reaches  1.75  and  occasionally  goes  as  high 
as  2.  According  to  Carl  G.  Barth,  the  ideal  value  for  this  ratio  is  the  fourth 
root  of  2  or  1.189.  It  should  not  be  more  than  1.25. 


DRIVING  SYSTEMS  FOR  MACHINE  TOOLS 


145 


reducing  the  ratio  between  the  highest  and  lowest  cone  speeds 
and  then  supplementing  this  reduced  ratio  with  additional  back 
gears  in  order  to  get  the  required  overall  range  of  speed,  thereby 
increasing  the  belt  speed  on  all  the  steps  but  most  on  the  large 
ones  where  most  needed.  The  effect  of  this  change  is  greater 
than  at  first  sight  appears  possible.  The  best  method  of  demon- 
strating the  effect  is  to  calculate  the  comparative  powers  with 
the  belt  on  the  larger  steps  of  the  two  pulleys  shown,  which  are 
from  actual  machines  and  which  are,  as  nearly  as  may  be,  of  the 
same  overall  dimensions  and  are  thus  fairly  comparable. 


2z    Belt 


4  "Belt 


FIG.  124. — Conventional  design  of  cone     FIG.    125. — Improved   design   of   cone 
pulley.  pulley. 

Calling  the  highest  belt  speed  in  Fig.  124 — that  obtained 
with  the  belt  on  the  four-inch  step — 100,  the  slowest— that  on 
the  twelve-inch  step — will  be:1 

100  X  TV  =  33l 

To  maintain  the  same  driven-cone  speed  the  highest  belt 
speed  in  Fig.  125  will  be: 

loo11**  =  288  + 

4 
and  the  lowest  will  be: 

288  X  ^f  =  255  + 
o 

1  The  counter-shaft  cone  is  assumed  to  be,  as  is  usual,  a  duplicate  of  the  machine 
cone. 

10 


146  METHODS  Of  MACHINE  SHOP  WORK 

The  smallest  step  of  Fig.  124  is  too  small  for  a  double  belt, 
while  the  reverse  is  true  of  Fig.  125.  To  obtain  the  ratio  of 
power  capacities  we  must  multiply  the  belt  speed  ratio  by  a 
suitable  ratio  for  the  double  belt,  say  ~,  and  also  by  the  ratio 

A 

of  the  belt  widths,  -^.     Doing  this  we  obtain: 

22 

Power  capacity  of  Fig.  125,  small  step  _  288      10      ^ 
Power  capacity  of  Fig.  124,  small  step       100       7  '    i\ 

Power  capacity  of  Fig.  125,  large  step  _  255       K>      _4_ 
Power  capacity  of  Fig.  124,  large  step      33^        7   '    i\  " 

That  is,  the  capacity  of  the  cone  shown  in  Fig.  1 2  5  on  the  small 
step  is  6|  and  on  the  large  step,  where  most  needed,  17 J  times 
that  of  the  one  shown  in  Fig.  I24.1  In  the  cases  shown,  there 
is  a  slight  increase  in  the  diameter  of  the  large  step  but,  without 
this  increase,  the  gain  would  be  nearly  as  large,  although  so 
large  a  gain  is  seldom  needed.  The  pulley  shown  in  Fig.  125 
gives  a  smaller  overall  range  of  speeds  and  a  smaller  number  of 
speeds  than  does  the  one  shown  in  Fig.  124.  Additional  back 
gears  are  needed  to  correct  both  deficiencies.  It  is  the  necessity 
for  these  gears  that  makes  feasible  the  reduced  number  of  cone 
steps  and  the  increased  width  of  belt. 

There  is  no  doubt  also  that  the  direct  connection  between  the 
cone  pulley  and  the  work  or  tool  spindle  has  been  retained  in 
many  cases  for  which  it  should  have  been  discarded.  With 
small,  light  power  machines  this  construction  is  satisfactory 
but,  as  the  size  of  the  work  increases,  it  ultimately  becomes 
inadequate,  since  with  it  the  belt  speed  is  too  low  to  carry  the 
power  required.  The  remedy  is  to  connect  the  cone  pulley  and 
spindle  through  gearing  and  thus  speed  up  the  pulley  and  belt. 
As  sizes  of  machines  increase  this  is  always  done  ultimately, 
but  the  change  is  commonly  deferred  too  long.  High  belt 
speed  costs  nothing  and  advantage  should  be  taken  of  the  in- 
creased power  that  goes  with  it.  Were  the  speeds  of  machine 
belts  two  or  three  thousand  feet  per  minute,  instead  of  as  many 
hundred,  there  would  be  no  deficiency  of  belt  power. 

1  The  first  publication  of  the  possibilities  of  improved  cone-pulley  design  was 
by  H.  M.  Norris. 


DRIVING  SYSTEMS  FOR  MACHINE  TOOLS  147 

DIFFICULTIES  INTRODUCED  BY  THE  INDIVIDUAL  MOTOR 
The  variable-speed  motor  drive  brought  in  its  train  many 
difficulties  to  the  machine-tool  maker,  these  difficulties  being 
chiefly  structural  and  due  to  lack  of  standardization  of  the 
motors.  Motors  from  different  makers  differed  in  the  ratio 
between  their  extreme  speeds  and,  since  the  ratio  of  the  sup- 
plementary back  gears  should  have  a  suitable  relation  to  the 
overall  speed  ratio  of  the  motor,  it  follows  that  any  change  in  the 
latter  involved  a  change  in  the  former  ratio.  Less  fundamental, 
but  scarcely  less  troublesome,  was  the  fact  that  motors  of 
different  makes  but  of  the  same  power  were  unlike  in  their 
leading  dimensions.  If  they  had  the  same  speed  ratio  the 
heights  to  the  shaft  centers  frequently  varied  as  did  the  sizes 
of  the  bases  and  the  positions  of  the  holding-down  bolt  holes. 
These  considerations  interfered  with  the  production  of  standard 
machines  by  requiring  the  adaptation  of  each  machine  to  its 
motor.  The  makers  found  it  no  longer  possible  to  make  and 
to  sell  from  stock  standard  machines,  special  adaptation  to 
the  specified  motor  being  required  in  each  case. 

THE  CONSTANT-SPEED  PULLEY  DRIVE 

This  was  an  impossible  condition  as  the  whole  industry  was 
based  upon  standardization,  and  the  constant-speed  pulley  sys- 
tem was  devised  to  meet  the  difficulty.  In  this  system  the 
first  motion  shaft  of  the  machine  is  arranged  to  be  driven  at  a 
constant  speed  which  is  easily  obtainable  from  any  constant- 
speed  motor  by  a  mere  selection  of  pulley  sizes  and  then,  added 
to  this,  is  a  set  of  gears  arranged  in  a  gear  box  and  fitted  with 
a  system  of  levers  by  which  the  change  of  speed  is  made  as 
easily  and  as  quickly  as  by  the  controller  of  the  motor.  The 
result  was  to  again  standardize  the  machines  and  to  give  them, 
from  the  makers'  standpoint,  the  enormous  advantage  of  equal 
adaptability  to  both  line  shaft  and  individual  motor  driving. 
Examples  of  the  constant-speed  pulley  drive  are  given  in  Figs. 
136,  163,  181,  182,  183,  216,  and  217. 

THE  CONE-PULLEY  BELT  SHIFTER 

For  the  milling  machine  the  constant  speed  drive,  as  explained 
at  length  in  the  chapter  on  milling,  has  peculiar  fitness  and  in 


148 


METHODS  OF  MACHINE  SHOP  WORK 


all  applications  it  provides  a  self-contained  machine,  whereas 
the  cone-pulley  drive  includes  a  detached  countershaft  for 
which,  in  shops  designed  for  individual  motor  driving,  it  is 
frequently  difficult  to  provide.  Nevertheless,  the  cone  pulley 


FIG.  126. — Mechanical  belt  shifter  for  cone  pulley  belts. 

is  too  simple,  cheap  and  adaptable  a  thing  to  be  discarded  and 
manufacturers  are  beginning  to  turn  their  attention  to  it  again. 
When  proportioned  in  the  manner  that  has  been  explained 
its  most  serious  original  defects — too  large  speed  intervals  and 
inadequate  power — disappear  and  it  only  remains  to  devise  a 


DRIVING  SYSTEMS  FOR  MACHINE  TOOLS  149 

convenient  mechanical  belt  shifter  to  give  it  all  the  operating 
qualities  of  either  the  variable-speed  motor  or  the  constant- 
speed  pulley  gear  box  drive,  together  with  a  lower  cost  than 
either  one. 

Fig.  126  shows  such  a  belt  shifter  applied  to  a  well  propor- 
tioned cone  pulley  by  the  R.  K.  LeBlond  Machine  Tool 
Company.1  The  author  ventures  to  predict  that,  through 
such  means  as  this,  the  cone  pulley  will  eventually  be  reha- 
bilitated as  a  leading  method  of  machine-tool  driving. 

THE  FIELD  OF  THE  INDIVIDUAL  MOTOR  DRIVE 

All  this  is  not  to  be  understood  as  meaning  that  the  individual 
motor  drive  has  no  place,  for  it  has  a  large  one.  For  portable 
floor  plate  tools  it  is  the  only  practicable  system.  For  isolated 
tools  and  for  others  so  located  that  line-shaft  layouts  for  their 
accommodation  are  inconvenient,  it  is  the  natural  and  proper 
recourse.  It  permits  the  locating  of  large  tools  under  travelling 
cranes  without  interference  with  the  runway  by  overhead 
structures,  and  for  such  tools  this  is  a  commanding  advantage. 
In  general,  flexibility  of  location  is  often  of  large  importance  in 
connection  with  large  tools,  while,  with  such  tools,  the  cost  of 
individual  motors  is,  relatively,  a  less  serious  item  of  additional 
cost  than  with  small  ones.  For  the  great  majority  of  small  and 
medium  sized  tools,  however,  no  inherent  advantage  has  been 
shown  to  attend  its  use.  It  has,  moreover,  unquestioned  and 
inherent  disadvantages,  chief  of  which  is  its  increased  cost,  both 
of  installation  and  of  operation. 

The  power  capacity  of  an  individual  motor  must  be  that  due 
to  the  maximum  requirement  of  the  machine  to  which  it  is 
attached.  Unlike  the  group  system,  in  which,  through  a  line 
shaft,  one  motor  drives  several  machines,  there  is  no  opportunity 
to  take  advantage  of  the  average  load.  Of  any  group  of 
machines  but  few  work  simultaneously  under  maximum  duty, 
while  at  all  times  a  considerable  percentage  is  normally  idle. 
The  result  is  that  the  average  requirement  of  such  a  group  is 
but  a  fraction  of  the  sum  of  the  maximum  requirements  of  the 

1  Mechanical  bell  shifters  were  fitted  to  the  cone  pulleys  of  the  Cornell  Univer- 
ity  shop  by  Dr.  Sweet  nearly  forty  years  ago. 


150  METHODS  OF  MACHINE  SHOP  WORK 

individual  tools.  Under  the  group  system  advantage  may  be 
taken  of  this  by  installing  a  motor  whose  normal  capacity  is 
equal  to  the  average  requirement  of  the  machines  to  be  driven 
by  it.  Under  the  individual  motor  system,  on  the  other  hand, 
we  have  several  much  smaller  motors  of  much  greater  aggregate 
capacity,  the  first  result  being  much  higher  initial  cost. 
Moreover,  since  the  large  group  motor  works  under  its  normal 
load,  or  very  near  it,  its  efficiency  is  high,  while  since,  at  any  one 
time,  most  of  the  individual  motors  work  under  loads  much 
below  their  normal,  their  efficiency  is  low,  the  second  result 
being  a  greater  consumption  of  current  and  the  necessity  for  a 
power  plant  of  greater  capacity. 

In  addition  to  the  cloud  under  which  it  unjustly  rests,  there 
are  serious  physical  difficulties  in  the  way  of  the  revival  of 
cone-pulley  driving.  Wisely,  or  unwisely,  many  customers 
want  individual  motor-driven  machines  and  many  modern 
shops  are  laid  out  with  its  use  in  view.  Machine-tool  makers 
cannot  be  criticised  for  supplying  machines  to  suit  the  demand, 
and,  with  the  constant-speed  pulley  drive  equally  adapted, 
without  change,  to  individual  motor  or  line  shaft  driving,  the 
reason  for  its  popularity  is  apparent.  Such  influences  as  these 
are  the  chief  determining  factors,  to  the  exclusion  of  considera- 
tions of  the  fundamental  merits  of  the  rival  systems. 


CHAPTER  VIII 

TURNING  AND  BORING 

The  primitive  engine  lathe — Lathes  for  work  of  large  diameter  and 
great  length — The  boring  mill,  plain  and  turret — The  turret  lathe — 
Special  tools  and  their  cost — The  collet  chuck — The  pilot  bar — Reamers 
and  reaming — The  automatic  turret  lathe — The  magazine  feed — The 
multiple  spindle  automatic  turret  lathe — The  multaumatic  machine — The 
Fay  and  Lo-swing  lathes — The  three  types  of  boring  bars  and  their  uses — 
Taper  and  spherical  boring  bars — Vertical  boring  machines  for  large 
engine  cylinders. 

THE  FIRST  SCREW-CUTTING  LATHE 

The  engine  or  screw-cutting  lathe  of  to-day  is  the  direct 
descendant  of  the  machine  shown  in  Fig.  I271  which  was  made 
by  Henry  Maudsley  about  1800  and  was  the  first  to  embody 
principles  that  are  now  universal.  Prior  to  Maudsley's  time, 
lathe  tools  were  controlled  by  the  hand  alone,  after  the  manner 
of  small-speed  lathes  of  to-day.  Like  all  great  inventions,  the 
slide  rest  which  here  appears  was  anticipated  by  the  work  of 
others  but  not  effectively,  while  the  connecting  of  the  work 
spindle  and  lead  screw  by  change  gears,  whereby  screw  cutting 
was  made  possible,  appears  in  none  of  these  anticipations. 
Maudsley  is  thus  commonly  and  correctly  credited  with  the 
invention  of  the  slide  rest.  As  the  author  interprets  Maudsley's 
work,  however,  the  invention  was  of  wider  scope  than  this, 
for  he  invented  other  machine  tools  embodying  the  same 
essential  principle  which,  broadly  speaking,  was  the  mechanical 
control  of  cutting  tools,  in  which  large  field  his  only  effective 
anticipation  was  the  boring  bar  of  Wilkinson  which  preceded 
the  lathe. 

Maudsley  was  also  the  first  to  cut  good  screws  and  substan- 
tially all  the  screws  of  to-day  are  the  lineal  descendants  to  the 
nth  generation  of  those  made  by  him.  He  made  a  machine2 

1  The  lathe  is  now  preserved  at  South  Kensington  Museum. 

2  Also  preserved  at  South  Kensington  Museum. 

151 


152  METHODS  OF  MACHINE  SHOP  WORK 

for  originating  screws  and  from  his  time  until  the  present  day 
improvement  in  the  accuracy  of  screws  has  been  brought  about 
chiefly  by  beginning  with  the  best  screw  available  as  a  lead 
screw  and  cutting  others  from  it  by  devices  which  corrected  its 
errors.  Modern  refined  methods  of  doing  this  have  already 
been  given.  True,  other  than  Maudsley's  methods  of  originat- 
ing screws  have  been  devised  and  used  for  precision  purposes, 
but,  measured  by  the  number  of  their  progeny,  their  influence 


FIG.  127.— Maudsley's  original  screw  cutting  lathe. 

has  been  small  compared  with  that  of  his  screws.  Small 
screws  are  also  still  occasionally  made  by  the  use  of  hand 
chasers  and  such  screws  have  no,  or,  at  most,  a  remote  con- 
nection with  Maudsley's,  but  they  are  small  in  size,  number 
and  importance. 

Maudsley  was  the  first  great  mechanic  in  the  modern  sense. 

LARGE  LATHES  AND  BORING  MILLS 

It  is  not  the  author's  purpose  to  discuss  engine  lathe  work 
in  general  with  which  the  reader  is  presumed  to  be  familiar. 


TURNING  AND  BORING 


153 


To  those  accustomed  to  work  of  small  and  medium  sizes  the 
forms  taken  by  lathes  for  large  work  are  somewhat  surprising. 
For  work  of  large  diameters  and  relatively  short  length  the 
machine  becomes  a  pit  lathe  of  which  a  fine  example  from  the 
works  of  the  Mesta  Machine  Company  is  shown  in  Fig.  128. 

When  positive  truth  is  required  in  turned  work  there  is  no 
method  of  mounting  it  equal  to  that  of  placing  it  on  a  mandrel 
as  in  the  present  example.  Pit  lathes,  however,  are  somewhat 


FIG.  128. — Pit  lathe  at  work. 

slow  and  the  weight  of  heavy  pieces  makes  their  placing  in 
position  troublesome.  For  work  of  large  diameter  a  much  more 
common  machine  is  the  boring  mill,  of  which  one  of  twenty  feet 
swing,  by  the  Betts  Machine  Company  is  shown  in  Fig.  129. 
Boring  mills  of  large  size  are  frequently  made  as  extension  mills 
—the  housings  being  arranged  to  be  drawn  back  on  the  base  in 
order  to  increase  the  capacity.  Such  an  extension  mill,  also 
by  the  Betts  Machine  Company,  of  sixteen  feet  swing  with  the 
housings  in  their  forward  and  of  twenty-four  feet  in  their  rear- 


154 


METHODS  OF  MACHINE  SHOP  WORK 


FIG.  129. — Twenty-foot  boring  mill. 


FIG.  130. — Sixteen-twenty-foot  extension  boring  mill. 


TURNING  AND  BORING 


155 


156  METHODS  OF  MACHINE  SHOP  WORK 

ward  position  is  shown  in  Fig.  130.  In  order  to  reach  the 
center  of  the  table  when  the  housings  are  run  back,  an  auxiliary 
removable  arm  perpendicular  to  the  cross  rail  is  provided. 

Unlike  all  other  machine  tools  the  boring  mill  developed 
from  the  top  downward.  Its  chief  advantage  over  the  pit 
lathe  is  that  the  work  does  not  have  to  be  chucked  in  opposition 
to  its  own  weight.  Lying  as  it  does  on  the  face  plate  of  the 
machine,  a  piece  may  be  adjusted,  without  the  difficulty  that 
attends  the  adjustment  of  heavy  work  in  the  lathe.  It 
was,  therefore,  first  developed  of  large  size  for  heavy  work, 
the  realization  of  its  advantage  over  the  lathe  leading  to  its 
later  production  in  progressively  smaller  and  smaller  sizes  and, 
ultimately,  with  the  addition  of  a  turret  for  the  production  of 
repetition  work. 

For  work  of  large  size  combined  with  great  length  the  gun 
lathe  shown  in  Fig.  131  from  the  Washington  Navy  Yard  will 
serve  as  an  example.  This  lathe,  by  the  Niles-Bement-Pond 
Company,  was  built  especially  for  the  construction  of  the  largest 
guns.  The  great  length  of  the  lathe  is  due  to  the  necessity  for 
accommodating  the  boring  bar,  since  the  lathe  bores  as  well  as 
turns  the  guns.  The  accommodation  of  this  bar  requires  the 
lathe  to  be  about  twice  as  long  as  it  would  be  were  it  required 
to  take  in  the  gun  only. 

THE  PLAIN  TURRET  LATHE 

The  adaptation  of  the  lathe  to  the  manufacturing  system  is  by 
the  turret  lathe  which  originated  with  the  Jones  and  Lamson 
Machine  Company  in  1855. 

A  simple  turret  lathe  by  the  Warner  and  Swasey  Company— 
the  principle  being  the  more  obvious  because  of  the  simplicity 
of  the  machine  shown — is  illustrated  in  Fig.  132.  The  basic  idea 
of  this  and  of  all  turret  lathes  is  to  preserve  the  setting  of  the 
tools  for  a  succession  of  pieces.  In  the  use  of  the  engine  lathe 
having  a  single  tool  post,  each  finishing  tool  is  of  necessity 
adjusted  with  great  nicety  as  each  cut  is  taken  but,  when  the 
next  cut  is  taken,  the  tool  must  be  removed  and  the  setting 
destroyed.  The  turret  lathe  preserves  the  setting  when  once 
made  by  providing  a  revolving  turret  having  several  holes  in 


TURNING  AND  BORING  157 

which  are  inserted  suitable  tool  holders.  After  a  cut  is  finished, 
the  turret  is  revolved  a  step,  thereby  presenting  the  next 
tool  to  the  work  without  destroying  the  adjustment  of  the  first, 
which  remains  ready  for  the  next  piece  when  its  turn  comes.  In 
addition  to  thus  duplicating  the  diameters  of  the  work,  the 
lengths  of  the  various  cuts  are  positively  determined  by  a  series 
of  adjustable  stops  which  are  seen  projecting  from  the  right 
of  the  turret  slide.  These  stops  form  a  lantern  which  revolves. 


FIG.  132. — Turret  lathe, 

step  by  step  with  the  corresponding  movements  of  the  turret,  in 
order  that  they  may  be  presented,  one  by  one  and  in  proper 
order,  to  a  stationary  stop  below  the  turret  slide. 

The  lathe  shown  has  a  hole  lengthwise  through  its  spindle  to 
adapt  it  for  work  from  the  bar,  as  the  expression  is — a  bar  of 
rough  stock  passing  through  the  spindle  and  being  pushed  for- 
ward and  then  gripped  in  the  chuck  by  the  lever  and  other 
mechanism  at  the  left  after  each  piece  has  been  finished  and  cut 
off.  For  this  latter  purpose  a  tool  slide  having  a  crosswise  move- 
ment only,  although  adjustable  lengthwise  of  the  lathe,  is  pro- 
vided. This  slide  is  fitted  with  two  tool  posts,  of  which  the 
one  in  the  rear,  fitted  with  an  inverted  tool,  may  be  used  for 
cutting  a  recess,  rounding  a  corner,  etc. 


158 


METHODS  OF  MACHINE  SHOP  WORK 


TURNING  AND  BORING  159 

The  turret  lathe  was  originally  made  for  the  production  of 
small  pieces — screws,  studs,  pins,  etc.,  from  the  bar,  but  it  has 
been  progressively  enlarged  until  machines  are  now  to  be  made 
capable  of  taking  bars  of  stock  of  eight  inches  diameter  through 
their  spindles.  Meanwhile,  another  adaptation  has  been  made 
by  the  provision  of  suitable  work  holding  chucks  whereby  sepa- 
rate castings  and  forgings  may  be  handled  and,  on  top  of  this, 
both  types  of  machines  are  now  made  to  perform  all  their  func- 
tions automatically,  the  work  of  the  operator  being  not  much 
more  than  keeping  them  supplied  with  stock. 

THE  TURRET  BORING  MILL 

The  turret  principle  is  also  applied  to  boring  mills  of  small 
and  medium  sizes,  such  machines  being  frequently  called  ver- 
tical turret  lathes.  A  machine  of  this  type  by  the  Bullard 
Machine  Tool  Company  is  shown  in  P'ig.  133.  A  supplementary 
cross-slide  turret  capable  of  carrying  four  tools  forms  an  addi- 
tional feature  of  this  machine  and  of  others. 

In  this  machine  a  departure  is  made  from  the  usual  construc- 
tion of  the  stops.  As  was  explained  in  connection  with  Fig. 
132,  the  stops  are  commonly  mechanical  and  positive — the 
moving  stop  abutting  against  its  stationary  mate.  Instead 
of  this  construction,  visual  or  observation  stops  are  here  used. 
Large  micrometer  dials  carrying  adjustable  indexes  are  attached 
to  the  feed  screw  shafts,  the  sizes  of  the  work  being  determined 
by  the  matching  of  these  indexes  against  stationary  indexes  as 
shown  in  Fig.  134.  To  avoid  confusion  the  faces  of  the  turret 
are  numbered,  as  are  the  indexes.  The  sizes  of  work  dealt  with 
make  the  use  of  the  usual  special  tools  set  for  the  outer  diameters 
impracticable.  The  tools  used  are  therefore  of  the  nature  of 
those  used  in  engine  lathes,  the  outer  diameters  as  well  as  the 
lengths  of  the  pieces  made  being  determined  by  the  observation 
stops. 

The  general  method  of  tooling  the  machine  and  attacking  the 
work,  combined  with  the  use  of  the  two  turrets,  is  shown  in  Fig. 
135.  Except  for  the  use  of  tools  of  the  lathe  type  for  the  outer 
diameters,  this  illustration  will  also  serve  to  show  the  application 


160 


METHODS  OF  MACHINE  SHOP  WORK 


of  the  turret  principle  to  small  as  well  as  large  work.  Two 
settings  for  the  opposite  sides  of  the  fly  wheel  are  shown,  the 
work  of  the  second  side  being  shown  in  the  two  right-hand 
views. 

A  prominent  example  of  the  turret  lathe  is  found  in  the  flat 
turret  lathe  of  the  Jones  &  Lamson  Machine  Company,  which  is 
the  legitimate  successor  of  the  original  turret  lathe.  In  this 
machine,  Fig.  136,  the  turret  is  a  flat  turn  table  carrying  the  tool 
holders  upon  its  top  instead  of  about  its  periphery.  These  tool 


Turret  Lay- 
out 2- Opera  t, 
2nd 'Setting 


urret  Lay 
out  8- Ope  ra- 
tions   Ist 
Setting 


7 th  Operation        2      Opera  tion 


3  "*  Operation  6 fh  Operation 


2  na  Opera  tion 

FIG.   135. — Representative  arrangement  of  turret  tools. 


holders  are  so  designed  as  to  take  simple  turning  and  boring 
tools,  somewhat  after  the  manner  of  the  tool  post  of  an  engine 
lathe  and  thus  reduce  the  amount  of  tool  making  required  and 
adapt  the  machine  to  the  production  of  parts  in  small  lots.  In 
addition  to  this,  long  pieces  may  be  made  as,  there  being  nothing 
in  the  way  to  prevent,  the  turret  may  pass  under  such  a  piece 
without  interference.  Another  feature  is  the  mounting  of  the 
head  stock  upon  a  cross  slide  which  performs  the  functions  of 
the  cross  slide  of  an  engine  lathe  and  permits  facing,  necking  and 
internal  undercutting  to  be  done. 


TURNING  AND  BORING  161 

This  machine,  like  others  that  follow,  is  driven  by  the  con- 
stant-speed pulley  system.  The  pulley  is  shown  at  the  left 
of  the  head  stock  which  forms  the  gear  box.  Within  it  is  a  sys- 
tem of  change  gears  which  are  manipulated  by  the  projecting 
hand  levers. 

The  cutting  tools  and  their  holders  for  turret  lathes  are  more 
or  less  special  and  made  for  the  particular  piece  of  work  to  be 
produced.  This  is  true  of  all  processes  for  manufacturing  parts 
in  lots.1 


FIG.   136.— Flat  turret  lathe. 

The  cost  of  such  tools  must  obviously  be  returned  through  the 
saving  which  they  accomplish — this  remark  applying  not  only 
to  the  cutting  tools  but  to  other  special  equipment  which  is 
characteristic  of  the  manufacturing  system. 

RELATION  OF  COST  AND  SAVING  DUE  TO  SPECIAL  TOOLS 

Very  little  has  been  published  from  which  the  principles  fol- 
lowed by  manufacturers  in  determining  the  justifiable  expense 
of  an  equipment  for  any  particular  case  can  be  deduced  and, 
indeed,  it  would  appear  that  not  many  manufacturers  have 

1  In  the  case  of  the  turret  lathe,  especially  the  flat  turret  lathe,  special  tools 
are  much  less  required  than  formerly. 
11 


162  METHODS  OF  MACHINE  SHOP  WORK 

definite  rules  for  this  work,  the  common  procedure  being  to 
determine  the  nature  of  the  equipment  by  the  exercise  of  simple 
judgment.  In  the  case  of  pieces  made  in  large  numbers,  for 
example  in  gun,  sewing  machine,  and  typewriter  work,  the 
judgment  of  a  competent  man  in  this  connection  is  usually 
sufficient.  In  work  of  this  character  the  saving  produced  by  an 
equipment  is  repeated  such  an  enormous  number  of  times,  that 
even  a  trifling  saving  on  each  piece  multiplied  by  the  number  of 
pieces  made,  produces  a  total  which  justifies  any  equipment 
within  reason. 

The  pinch  comes  in  connection  with  work  produced  in  smaller 
numbers  in  which  the  saving  on  one  piece  is  repeated  a  limited 
number  of  times.  In  work  of  this  kind  the  cost  of  the 
equipment  must  be  considered  in  relation  to  the  saving  due  to 
it  and,  for  such  work,  the  author  adopted  a  rule  many  years  ago 
that  the  estimated  saving  due  to  a  given  special  equipment 
should  return  its  estimated  cost  in  one  year's  time  and  that  if  it 
failed  to  promise  such  a  return  it  should  not  be  made.  This 
rule  will  impress  most  readers  as  extremely  drastic  and  it  was, 
indeed,  made  drastic  for  special  reasons.  There  are,  however, 
reasons  of  perfectly  general  application  which  make  it  necessary 
that  such  a  rule  should  be  more  drastic  than  would  at  first 
sight  appear.  The  rule  is  based  upon  estimated  cost  and 
estimated  savings.  One  sometimes  goes  wrong  in  his  estimates 
and,  more  often  than  not,  the  error  is  in  the  wrong  direction. 
Moreover,  one  never  knows  when  an  improvement  will  come 
along  which  will  lay  a  fine  lot  of  special  tools  on  the  scrap  heap. 
If  a  set  of  tools  continues  in  use  four  years,  which  is  longer  than 
the  average,  they  must  earn  twenty-five  per  cent,  per  annum 
to  replace  themselves  and  they  must  also  earn  enough  to  keep 
themselves  in  repair  and  it  is  not  until  they  have  done  these 
things  that  profit  begins.  For  these  reasons  the  author  is 
convinced  that,  as  a  general  rule,  subject  to  occasional  reduc- 
tion in  cases  where  there  is  little  probability  of  revolutionary 
improvements,  special  tools  should  return  by  their  savings  not 
less  than  fifty  per  cent,  of  their  cost  per  annum.  On  the  other 
hand,  in  an  industry  which  is  in  process  of  rapid  development, 
this  percentage  should  be  increased. 


TURNING  AND  BORING 


163 


Whatever  the  percentage  adoped,  a  rule  in  this  form  is  of 
perfectly  general  application.  It  takes  account  not  only  of  the 
size  of  the  lots  and  of  the  lost  time  due  to  setting  up  and  adjust- 
ing the  machines,  but  also  of  idle  periods  between  lots,  regardless 
of  their  length. 

THE  COLLET  CHUCK 

An  important  feature  of  the  turret  lathe  is  the  collet  chuck, 
shown  in  its  original  form  in  the  section  of  the  head  stock  of  a 
precision  bench  lathe  by  Hardinge,  Brothers  in  Fig.  137  the 
chuck  proper  being  shown  to  an  enlarged  scale  below  thela  the 
head  stock.  The  spindle  of  the  lathe  is  bored  and  the  end  of  the 


x"'x*^     \ 

»/WWVV\A\VK. 

]      r 

wvwvww/* 

_l__jr_L-_  >— 

\ 

FIG.  137.— Collet  chuck. 

chuck  is  turned  to  an  angle.  The  chuck  is  split  by  three  radial 
slots  and  has  a  threaded  portion  at  its  rear.  A  tube  a  is 
threaded  to  fit  the  threads  on  the  chuck  and  carries  at  its  left  a 
hand  wheel.  The  turning  of  the  hand  wheel  draws  the  chuck 
within  the  lathe  spindle  and  closes  its  jaws  upon  the  work.1 

1  The  collet  chuck  was  originally  designed  for  watch  and  watch  tool  work. 
From  a  capacity  suitable  for  work  of  this  character  it  has  grown  step  by  step 
until  it  has  been  made  capable  of  taking  in  solid  steel  bars  of  eight  inches  diameter 
suitable  for  locomotive  crank  and  cross-head  pins. 


164 


METHODS  OF  MACHINE  SHOP  WORK 


In  the  adaptation  of  the  chuck  to  large  work  a  number  of 
modifications  have  been  made.  In  the  form  shown  in  Fig.  137 
it  is  known  as  the  draw-back  collet  chuck.  In  some  cases  the 


FIG.   139.— Modified  collet  chuck. 

taper  is  reversed,  resulting  in  the  push-out  chuck  shown  in  Fig. 
138  from  a  Bardons  and  Oliver  turret  lathe  from  which  the 
modification  will  be  apparent.  The  gripping  action  in  this  case 


TURNING  AND  BORING 


165 


is  no  longer  by  the  hand  wheel  shown  in  Fig.  137,  which  is  only 
used  in  connection  with  work  of  small  and  moderate  size.  The 
gripping  is  here  through  the  bell  cranks  a,  b,  the  sliding  collar  c, 


FIG.  140. — Collet  chuck  for  work  of  large  diameter. 


FIG.   141. — Construction  of  chuck  shown  in  Fig.  140. 

the  tube  d,  and  the  connected  mechanism.  In  the  act  of 
gripping  the  work  the  draw-back  chuck  draws  the  piece  toward 
the  head  stock  a  slight  distance.  Frequently  this  is  of  no 


166  METHODS  OF  MACHINE  SHOP  WORK 

importance  but  in  cases  in  which  pieces  are  required  to  be  of  an 
exact  length  it  interferes  with  this  requirement.  In  turret- 
lathe  work  from  the  bar  the  length  is  gaged  by  pushing  the  bar 
through  the  lathe  spindle  until  it  abuts  against  a  stop  in  the  first 
hole  of  the  turret.  With  the  bar  thus  abutting,  the  push-out 
chuck  cannot  disturb  its  position  and  for  such  work  it  is  some- 
times necessary  and  usually  to  be  preferred. 

By  a  suitable  modification  of  its  construction  the  chuck  has 
been  adapted  to  the  chucking  of  separate  castings  or  forgings 
of  considerable  size.  Fig.  139  shows  such  a  modification  of  the 
draw-back  chuck,  this  illustration  also  being  from  Bardons  and 
Oliver.  The  collet  a  carries  false  jaws  b  which  are  adapted  to 
the  diameter  of  the  work  to  be  done.  The  closing  of  the  jaws 
is  accomplished  by  the  action  of  a  tube  through  the  spindle  of 
the  lathe,  but  for  still  larger  work  this  becomes  impracticable 
and  the  construction  of  Figs.  140  and  141  is  adopted.  In  this 
case  the  increased  diameter  leads  to  the  introduction  of  an  in- 
creased number  of  cuts  in  the  collet  which  are  made  alternately 
from  the  two  ends.  The  closing  of  the  collet  is  by  the  action 
of  the  outer  threaded  ring  on  the  body  of  the  chuck.  In  this  as  in 
the  last  construction  the  work  is  seldom  gripped  directly  by  the 
collet  faces.  False  jaws  are  usually  inserted  in  the  collet  and 
are  bored  to  suit  the  work  to  be  done. 

THE  PILOT  BAR 

An  important  feature  of  turret-lathe  equipment,  known  as  the 
pilot  bar,  was  introduced  by  the  Gisholt  Machine  Company. 
The  action  of  this  appliance  will  be  understood  from  Figs.  142 
and  143,  although  these  illustrations  are  not  from  a  Gisholt 
lathe.  The  work  in  progress  is  the  turning  of  the  face  of  a  bevil 
gear  blank  a  by  means  of  the  broad-faced  tool  b,  in  Fig.  142 
without  and  in  Fig.  143  with  the  pilot  bar  c.  In  Fig.  142  thf 
strain  due  to  the  pressure  of  the  cut,  starting  at  the  arrow  d, 
follows  the  dotted  line  through  the  tool  support,  the  lathe  bed, 
the  spindle,  and  the  work  to  the  reaction  arrow  e.  This  round- 
about course  of  the  strain  leads  to  spring  and  chatter  which 
are  largely  eliminated  by  the  use  of  the  pilot  bar  as  shown  in  Fig. 


TURNING  AND  BORING 


167 


143,  in  which  the  dotted  line  again  shows  the  path  of  the  strain 
due  to  the  pressure  of  the  cut.  With  this  construction  the  strain 
does  not  reach  the  frame  of  the  machine  at  all,  the  more  limited 
area  which  it  occupies  and  the  reduced  leverage  by  which  it 


FIG.  142.  FIG.  143. 

Principle  of  the  pilot  bar. 


FIG.  144. — Use  of  the  pilot  bar. 

acts  serving  to  greatly  reduce  its  effect  and  to  increase  the  capac- 
ity for  heavy  work. 

The  pilot  bar  is  more  frequently  made  to  support  the  cutting 


168 


METHODS  OF  MACHINE  SHOP  WORK 


tool ,  thereby,  in  another  way,  increasing  the  capacity  for  heavy 
cuts.  Such  a  use  of  it  is  shown  in  Fig.  144  which  illustrates  a 
heavy  turret  lathe  by  the  Niles-Bement-Pond  Company.  In 
this  case  the  tool  for  boring  a  gear  blank  is  inserted  in  the  middle 
of  the  pilot  bar  which,  fitting  a  suitable  bush  in  the  work-holding 
chuck,  is  much  more  favorably  supported  to  resist  the  strains 
upon  it  than  if  the  bar  were  cut  off  just  beyond  the  tool. 

REAMERS  AND  REAMING 

An  important  tool  in  turret-lathe  equipment  is  the  reamer  by 
which  the  sizes  of  holes  are  finished  and  maintained  uniform. 


FIG.  145. 


FIG.  146. 


FIG. 149. 


FIG.  147 


FIG.  148. 


Various  forms  of  reamers. 


FIG.  150. 


A  collection  of  reamers  of  various  types  adapted  to  various  uses 
and  conditions  is  shown  in  Figs.  145-150.  Fig.  145  shows  a 
fluted  reamer,  called  chucking  reamer,  in  which  the  reamer  and 
its  shank  are  in  one  piece.  The  reamer  is  slightly  tapered  at 


TURNING  AND  BORING  169 

its  outer  end,  the  cutting  action  being  upon  the  sides.  As  the 
size  increases  the  reamer  is  made  with  a  hole  through  it,  and 
its  shank  is  made  of  a  separate  piece.  Such  reamers,  shown 
in  Fig.  146,  are  called  shell  reamers.  Their  action  is  precisely 
the  same  as  that  of  the  tool  shown  in  Fig.  145. 

A  tool  having  somewhat  the  appearance  of  the  fluted  reamer 
but  an  entirely  different  action  is  shown  in  Figs.  147  and  148, 
the  tools  referred  to  being  called  rose  reamers.  As  before,  the 
small  sizes  are  made  integral  with  their  shanks  while  larger  ones 
are  separate.  The  flutes  of  these  tools,  while  in  appearance  like 
those  of  the  previous  reamers,  are  essentially  different  in  that 
they  do  no  cutting.  The  cutting  is  entirely  at  the  end  of  the 
reamer,  the  flutes  being  provided  as  channels  for  the  chips. 
Of  these  two  types,  the  fluted  reamer  is  commonly  used  for  the 
last  or  sizing  cut  for  which,  if  in  good  condition,  it  gives  a  beauti- 
fully finished  as  well  as  a  true  surface.  The  rose  reamer  is 
used  as  a  preparatory  tool,  its  cut  being  taken  just  previous 
to  that  of  the  fluted  reamer.  The  size  of  the  two  differs  enough 
to  give  a  light  finishing  cut  for  the  final  operation. 

Because  of  its  light  duty  the  fluted  reamer  will  remain  sharp 
and  maintain  its  size  a  long  time  but,  ultimately,  it  becomes 
dull  and,  when  sharpened,  its  size  is  reduced.  To  meet  this 
condition  a  large  amount  of  ingenuity  has  been  expended  in 
devising  adjustable  or  expansion  reamers  which  are  of  two  types. 
The  first  type  is  intended  to  be  expanded  or  contracted  to 
accommodate  small  changes  in  the  diameter  of  the  work, 
usually  by  a  screw  adjustment,  while  the  second  type  is  intended 
to  be  expanded  before  regrinding,  then  ground  to  its  original 
size  and  used  as  before,  precisely  as  though  it  were  a  solid 
reamer — this  operation  being  repeated  at  each  regrinding. 
While  some  will  dispute  the  statement,  the  author  believes, 
nevertheless,  that  the  first  type  of  reamer  is  not,  in  most  hands, 
a  success  while  the  second  type  is  a  success. 

An  expansion  reamer  of  the  second  type  is  shown  in  Fig.  149. 
The  cutting  blades  are  here  separate  from  the  body  of  the 
reamer  and  inserted  in  the  latter  in  dovetailed  slots.  The 
blades  and  the  slots  are  inclined  to  the  center  line  on  their  inner 
surfaces  in  order  to  provide  the  expansion  feature.  When  the 


170  METHODS  OF  MACHINE  SHOP  WORK 

reamer  becomes  dull,  the  blades  are  driven  up  the  slots  a  slight 
distance  and  the  reamer  is  then  placed  in  a  grinding  machine, 
reground  to  its  original  size,  and  backed  off  to  provide  suitable 
clearance. 

Another  tool  which  is  used  in  connection  with  reaming  opera- 
tions, called  the  four-lip  drill  or  four-lip  reamer,  is  shown  in 
Fig.  150.  Twist  drills  or,  for  that  matter,  all  drills  having 
two  cutting  edges,  have  no  tendency  to  straighten  holes  which 
are  once  wrongly  started  and,  if  used  to  enlarge  a  cored  hole,  they 
will  follow  the  eccentricity  of  the  hole.  The  four-lip  drill 
largely  corrects  this  tendency,  the  action  of  the  two  additional 
cutting  edges  being  to  oppose  a  resistance  to  the  tendency  due 
to  an  untrue  hole  to  deflect  the  drill  sidewise.  When  using 
such  a  tool,  if  the  hole  is  deep  and  the  drill  correspondingly 
long  and  flexible,  it  is  necessary,  when  starting  to  enlarge  a 
cored  hole,  to  precede  the  four-lip  drill  with  a  short  stiff  tool 
in  order  that  the  eccentricity  of  the  cored  hole  may  be  corrected 
by  starting  the  hole  correctly.  With  the  hole  begun  in  this 
manner,  the  four-lip  drill  may  be  brought  into  action  and, 
unlike  the  two-lipped  drill,  it  will  follow  the  true  start  regard- 
less of  the  deflecting  action  of  the  untrue  cored  hole.  The  hole 
being  made  straight  in  this  manner,  the  four-lip  drill  is  followed 
by  the  rose  and  fluted  reamers  in  turn.  The  four-lip  drill  is 
used  for  enlarging  holes  only.  It  will  not  drill  from  the  solid. 

FLOATING  REAMER  HOLDERS  AND  HAND  REAMING 

When  good  results  are  required,  the  final  reamer  must  be 
provided  with  a  flexible  support  whereby  it  is  free,  within  narrow 
limits,  to  adjust  itself  in  line  with  the  hole  as  prepared  for  it. 
Even  though  the  alignment  of  the  lathe  may  be  of  the  highest 
degree  of  accuracy,  there  will  be  enough  untruth  of  alignment 
of  the  lathe  or  of  the  hole  to  affect  the  finished  hole  if  the  reamer 
is  clamped  rigidly  in  the  turret  after  the  manner  of  the  other 
tools,  holes  reamed  in  this  manner  being  commonly  somewhat 
larger  than  intended  and,  more  likely  than  not,  larger  at  one 
end  than  at  the  other. 

Holders  arranged  to  permit  this  minute  adjustment  of  itself 


TURNING  AND  BORING 


171 


by  the  reamer  are  called  floating  reamer  holders.  They  are  made 
in  a  great  variety  of  forms,  one  of  which  is  shown  in  Fig.  151, 
The  holder  is  inserted  in  the  hole  of  the  turret,  the  reamer 
being  driven  by  the  movable  or  floating  feature  a. 

With  the  best  of  these  devices  there  is  always  some  resistance 
to  the  sidewise  adjustment  of  the  reamer  due  to  the  friction 
caused  by  the  force  required  to  hold  the  reamer  from  turning. 
For  this  reason  the  best  results  are  obtained  by  doing  the  ream- 
ing operation  by  hand.  With  the  reamer  put  through  its  hole 
by  a  hand-driven  wrench,  it  is  obviously  perfectly  free  to  adjust 
itself  to  the  existing  alignment  of  the  hole  and  thus  produce  a 
hole  of  its  own  size.  For  this  reason  one  often  sees  the  speci- 
fication, "hand  reaming  only,"  which  is  intended  to  and  does 
lead  to  superior  work. 


SECTION  A-O-B 

FIG.  151. — Floating  reamer  holder. 


SECTION  C-D 


The  author  is  aware  of  but  one  equipment  by  which  reaming 
may  be  done  by  power  and  with  the  same  accuracy  as  by  hand. 
This  equipment  is  shown  in  Fig.  152,  from  the  Detroit  works 
of  the  Chicago  Pneumatic  Tool  Company.  The  equipment 
consists,  first,  of  a  cast-iron  bench  which  is  used  for  no  other 
purpose  than  reaming  and  which  is  fitted  with  oil  supply  and 
drain  pipes  connected  with  the  oil  circulating  system  of  the 
factory.  The  reamer  is  driven  by  a  compressed  air  motor 
suspended  from  the  ceiling  by  a  cord,  pulley  and  balance  weight. 


172  METHODS  OF  MACHINE  SHOP  WORK 

The  reaction  due  to  the  driving  effort  of  the  motor  is  resisted 
by  the  two  hands  of  the  operator  applied  to  the  horizontal 
handles.  Both  driving  effort  and  resistance  are  true  moments 
without  side  pressure,  by  reason  of  which,  and  perhaps  even 
more  than  with  hand  reaming,  the  reamer  is  at  perfect  liberty 
to  follow  the  hole. 


FIG.  152. — Compressed  air  reaming  bench. 

THE  AUTOMATIC  TURRET  LATHE 

The  most  interesting  of  all  machine  tools  in  the  almost 
human  intelligence  which  it  shows  is  the  automatic  turret 
lathe1  which  was  developed  to  a  state  of  practical  usefulness 
chiefly  by  Christopher  M.  Spencer,  who  made  his  first  machine 

1  Frequently  called  automatic  screw  machine. 


TURNING  AND  BORING 


173 


about  1875.  A  prior  patent  by  Francis  Curtis  issued  in  1871 
and  another  by  L.  W.  Langdon  issued  in  1864  anticipate  some 
features  of  Mr.  Spencer's  work.  For  several  years  the  machine 
was  not  offered  for  sale  but  was  used  exclusively  in  the  works 
of  the  Hartford  Machine  Screw  Company. 

An  automatic  turret  lathe  by  the  Pratt  and  Whitney  Com- 
pany is  shown  in  Fig.  153,  for  which,  like  the  hand-operated 


FIG.  153. — Automatic  turret  lathe. 

machine,  a  simple  example  has  been  chosen  in  order  to  more 
clearly  illustrate  the  principle.  So  far  as  the  mounting  and 
action  of  the  cutting  tools  are  concerned,  this  machine  is  sub- 
stantially identical  with  the  hand-operated  machine,  but  the 
reciprocation  and  revolution  of  the  turret,  the  feeding  inward 
and  gripping  of  the  bar  of  stock,  and  the  action  of  the  cutting- 
off  tool  are  automatically  performed  by  means  of  the  cams 


174 


METHODS  OF  MACHINE  SHOP  WORK 


attached  to  the  drums  which  are  mounted  on  a  shaft  extending 
through  the  base  of  the  machine.  In  addition  to  this,  the  rate 
of  feed  of  the  various  tools  is  changed  from  tool  to  tool  in  order 
adapt  the  speed  to  the  individual  cutting  operation  and  the 
direction  of  revolution  is  reversed,  in  order  to  withdraw  a 
threaded  portion  from  the  die  which  cuts  the  threads.  The 


FIG.  154. — Magazine    feed    automatic  turret  lathe. 

speed  of  the  machine,  as  a  whole,  is  changed  by  cone  pulleys  on 
the  main  and  countershafts. 

The  work  spindle  and  the  drum  shaft  are  independently 
driven  in  order  that  their  speeds  may  be  independently  adjusted. 
The  speed  of  the  drum  shaft  has  no  fixed  relation  to  the  speed 
of  the  spindle,  but  is  so  adjusted  that  the  drum  shaft  makes 
one  complete  turn  while  one  piece  is  being  made,  regardless 
of  the  length  of  time  required  for  its  making.  Starting  at  the 
left,  the  first  drum  carries  a  series  of  cams  by  the  action  of  which 


TURNING  AND  BORING  175 

the  collet  chuck  is  loosened  and  tightened  and  the  bar  of  stock 
is  pushed  forward  after  the  cutting  off  of  each  piece.  The  next 
cam  manipulates  the  belt  shipper  which  controls  two  belts. 
The  middle  pulley  upon  the  work  spindle  is  the  driving  pulley, 
the  two  outer  ones  being  loose.  One  of  the  two  belts  is  com- 
monly crossed  and  serves  to  withdraw  a  threaded  piece  from  its 
die.  The  cam  in  the  middle  of  the  machine  operates  the  cross 
slide  which  carries  a  cutting-off  tool  and  also,  in  a  second  tool 
post  if  need  be,  a  necking  or  rounding  tool.  The  next  cam  drum 
at  the  right  actuates  the  turret  slide.  The  return  of  the  turret 
is  much  quicker  than  the  cutting  movement  which  latter  has,  if 
need  be,  a  quick  preliminary  movement  up  to  the  point  where  the 
cutting  action  begins.  At  the  extreme  right  is  a  cam  drum  by 
which  the  speed  of  rotation  of  the  cam  shaft  is  varied,  for  the 
slow  feeding  and  quick  return  movements  of  the  turret.  The 
camming  of  these  machines  for  various  kinds  of  work  is  very 
much  of  an  art.1 

THE  MAGAZINE  FEED  AUTOMATIC  TURRET  LATHE 

A  more  recent  development  of  the  automatic  turret  lathe, 
first  made  by  the  Pratt  and  Whitney  Company,  lies  in  its  adap- 
tation to  the  machining  of  separate  pieces  by  taking  them  one 
by  one  from  a  magazine,  inserting  them  in  a  chuck,  machining 
and  finally  rejecting  them  and  supplying  the  chuck  with  an- 
other. So  far  as  automatic  pushing  inward  a  bar  of  stock  is 
concerned,  the  work  does  not  differ  except  as  regards  the  size 
of  the  bar.  Individual  castings  and  forgings  are,  however,  of 
such  a  wide  diversity  of  form  that  various  kinds  of  magazines 
and  as  many  methods  of  handling  the  pieces  are  required,  the 
provision  of  which  often  requires  the  exercise  of  much  ingenuity. 

Fig.  154  shows  the  machine  as  arranged  for  the  first  piece 
of  work  to  which  it  was  adapted,  the  machining  of  the  small  belt 
pulleys  of  sewing  machines.  A  magazine,  filled  with  blank 
pulleys,  is  shown  above  the  work  spindle,  the  work  of  the  operator 
being  to  see  to  it  that  this  magazine  does  not  get  empty.  By 

1  Full  particulars  of  the  methods  of  laying  out  these  cams  may  be  found  in 
Automatic  Screw  Machines  and  their  Tools  by  C.L.  Goodrich  and  F.  A,  Stanley. 


METHODS  OF  MACHINE  SHOP  WORK 


•a 

oj 

SP 

IP 


TURNING  AND  BORING  177 

reason  of  the  inclination  of  the  magazine,  the  wheel  blanks  roll 
to  the  outlet  at  the  bottom,  from  which  point  a  transfer  carrier, 
operated  by  a  special  cam  upon  the  cam  shaft,  takes  them,  one 
by  one,  and  transfers  them  to  a  point  in  front  of  the  spindle 
chuck,  into  which  they  are  pushed  by  the  first  movement  of 
the  turret  and  then  gripped  by  an  additional  cam  action. 
When  the  piece  is  finished  it  is  automatically  released  from  the 
chuck  and  drops  out  on  the  floor,  as  shown,  when  its  place  is 
taken  by  another  through  the  action  of  the  transfer  carrier. 

It  is  impossible  to  include  any  considerable  number  of  the 
numerous  forms  of  magazine  and  of  transfer  mechanism  which 
have  been  devised  to  handle  pieces  of  various  forms.  One 
additional  construction  which  has  been  designed  to  handle 
pieces  of  a  wide  diversity  of  forms  is  shown  in  Figs.  155  and  156. 
Comparison  with  Fig.  154  will  serve  to  indicate  the  variety  of 
constructions  that  have  been  employed  to  meet  the  numerous 
conditions  that  present  themselves. 

This  construction  is  supplied  with  the  automatic  turret  lathes 
of  the  Cleveland  Automatic  Machine  Company.  Unlike  all 
others,  the  turrets  of  these  machines  turn  upon  a  horizontal 
center  line.  Structurally  the  turret  is  a  long  drum  supported 
by  a  barrel  casing  within  which  it  turns  and  slides.  The  end 
of  the  turret  appears  at  a  in  both  views,  projecting  from  its 
barrel  support  and  carrying  the  cutting  tools  and  the  transfer 
carrier,  b. 

The  magazine  consists  of  a  frame  c  mounted  on  a  shaft  d 
on  which  it  is  automatically  oscillated  between  the  positions 
shown  in  the  two  illustrations  by  a  suitable  cam.  Surround- 
ing the  frame  is  an  endless  link  belt,  each  link  of  which  is  formed 
into  a  hub.  Each  hub  has  a  hole  through  it  endwise  in  which  is 
inserted  a  bush  suitable  for  the  pieces  of  work  to  be  handled,  the 
pieces  in  this  instance  being  studs,  shown  projecting  from  the 
hubs.  The  studs  are  to  have  turning  and  threading  operations 
performed  on  their  projecting  ends.  With  the  magazine  tilted 
to  the  position  of  Fig.  155,  the  turret  advances,  when  the  trans- 
fer carrier  withdraws  the  opposing  piece  of  work  from  the  maga- 
zine and  at  the  next  movement  of  the  turret  transfers  it  to  and 

inserts  it  in  the  chuck.     Meanwhile  the  magazine  returns  to 
12 


178  METHODS  OF  MACHINE  SHOP  WORK 

the  position  of  Fig.  156  in  order  to  get  out  of  the  way  of  the 
cutting  tools,  and  remains  there  while  the  piece  is  being  machined 
and  until  the  time  arrives  for  the  next  piece  to  be  transferred  to 
the  chuck,  when  the  magazine  tilts  to  its  downward  position 
again.  During  this  downward  movement  the  long  pawl  e 
engages  one  of  the  pins  in  the  sprocket  wheel  /  by  which  the 
link  belt  is  driven  and  thus  advances  the  belt  and  its  load  of 
studs  one  link  and  presents  a  fresh  stud  to  the  transfer  carrier. 
In  Fig.  156  one  stud  is  seen  in  the  transfer  carrier  and  another  in 
the  chuck,  the  latter  having  had  the  turning  and  threading 
operations  upon  it  performed.  The  die  with  which  the  thread 
was  cut  occupies  a  hole  in  the  turret  in  line  with  the  second  stud. 

THE  MULTIPLE-SPINDLE  AUTOMATIC  TURRET  LATHE 

Another  comparatively  recent  development  of  the  automatic 
turret  lathe  is  found  in  the  multiple-spindle  automatic  turret 
lathe  which,  although  now  made  by  several  parties,  was  invented 
by  E.  C.  Henn  of  the  National  Acme  Manufacturing  Company. 
In  the  automatic  machine  as  so  far  shown,  the  various  opera- 
tions on  a  piece  are  successive,  the  time  required  to  make  a 
piece  being  the  sum  of  the  times  required  for  the  individual 
operations.  In  the  multiple-spindle  machine  four  pieces  are 
acted  upon  at  once  and  the  time  required  to  complete  the 
piece  becomes  that  of  the  longest  single  operation.1 

Referring  to  Fig.  157  which  shows  the  machine  of  the  National 
Acme  Manufacturing  Company,  we  see  at  the  extreme  left  four 
bars  of  hexigon  stock  which  pass  through  the  same  number  of 
hollow  work  spindles.  The  spindles  are  mounted  and  turn 
within  a  drum  which  is  mounted  within  the  cylindrical  head 
stock  and  which,  at  the  completion  of  each  operation,  makes  a 
quarter  turn  and  thus  shifts  the  bars  of  stock  to  the  successive 
operating  positions.  At  the  right  and  in  line  with  the  work 
spindles  are  four  tool  supports  which,  while  stationary  in  posi- 
tion, revolve  about  their  individual  centers  if  need  be.  A  more 

1  In  some  cases  even  this  is  reduced  by  dividing  the  longest  single  operation 
into  two,  thereby  making  the  time  required  that  of  one -half  the  longest  or  the 
entire  time  of  the  next  to  the  longest  single  operation,  in  case  that  exceeds  one- 
half  the  time  required  for  the  longest. 


TURNING  AND  BORING 


179 


FIG.  157. — Multiple  spindle  automatic  turret  lathe. 


FIG.  158.— Arrangement  of  tools  in  multiple  spindle  automatic  turret  lathe. 


180  METHODS  OF  MACHINE  SHOP  WORK 

complete  view  of  the  tool  supports  with  various  tools  mounted 
therein  is  given  in  Fig.  158,  in  which  are  also  shown  surrounding 
tool  slides  carrying  cutting-off,  necking  and  forming  tools 
which  act  simultaneously  with  the  revolving  tools,  two  opera- 
tions at  each  station  being  frequently  in  progress. 

The  term  turret  lathe  as  applied  to  this  machine  is,  in  a  sense, 
a  misnomer.  The  essential  feature  of  the  turrent  lathe — the 
mounting  of  the  tools  in  a  revolving  turret  and  turning  them  out 
of  and  into  the  cutting  position  as  required — is  not  found  in  this 
machine,  in  which  the  positions  of  the  tools  are  fixed.  On  the 
other  hand,  the  position  of  the  work  is  changed  by  presenting  it 
in  succession  to  the  various  tools  in  their  fixed  positions.  It 
would  more  properly  be  called  a  station  machine  to  indicate 
that  the  work  is  shifted  from  station  to  station  at  each  of  which 
an  operation  is  performed.  Looked  at  in  this  way,  this  machine 
was  the  forerunner  of  a  system  of  machines  which,  made  at 
home  for  special  purposes,  have  appeared  from  time  to  time, 
and  which,  as  the  multaumatic  vertical  lathe  of  the  Bullard 
Machine  Tool  Company,  has  now  made  its  appearance  as  a  gen- 
eral purpose  machine.  The  author  anticipates  and  predicts 
that  machines  of  this  type  will  form  the  next  large  development 
in  machine-shop  productive  equipment. 

The  Bullard  Multaumatic  machine  is  shown  in  Fig.  159.  The 
work-holding  chucks,  of  which  there  are  six,  are  mounted  in  a 
revolving  ring,  the  spindles  being  driven  from  below.  Five 
tools  are  mounted  on  the  upright  column,  the  sixth  station  being 
the  loading  station.  A  piece  of  work  being  fixed  in  the  chuck 
at  this  point,  the  first  step  movement  of  the  ring  brings  the  work 
below  the  first  tool  and  while  this  tool  is  operating  a  second 
piece  is  inserted  in  the  second  chuck  and  so  on  until  all  the 
chucks  are  full.  Thereafter,  as  each  chuck  arrives  at  the  load- 
ing station  with  the  work  on  its  piece  completed,  it  is  removed 
and  another  substituted  in  its  place,  the  operation  thereafter 
being  continuous  with  five  cuts  in  progress  at  all  times. 

AUTOMATIC  LATHES  FOR  WORK  DONE  BETWEEN  CENTERS 

It  will  be  observed  that  all  of  the  applications  of  the  turret 
lathe  shown  are  for  work  made  from  the  bar  or  for  pieces  of  a 


TURNING  AND  BORING 


181 


nature  which  can  be  held  in  a  chuck.  The  application  of  the 
turret  principle,  the  preservation  of  the  adjustment  of  the 
cutting  tools,  to  work  which  must  be  held  between  centers  is 
a  much  more  difficult  problem,  the  solution  of  which  came 
much  later.  The  customary  form  of  turret  is  entirely  inappli- 
cable because  the  tools,  which  project  radially  from  the  turret, 


FIG.  159. — Station  machine  for  lathe  work. 

interfere  with  the  head  and  tail  stocks.  Two  very  successful 
machines  for  this  purpose  are  the  Fay  and  the  Lo-swing  auto- 
matic lathes. 

The  Fay  lathe,  Figs.  160  and  161,  is  intended  more  espe- 
cially for  turning  pieces  which  are  carried  on  mandrels  while  the 
Lo-swing  lathe,  Fig.  163,  is  for  turning  pieces  of  considerable 


182  METHODS  OF  MACHINE  SHOP  WORK 


FIGS.  1 60  and  161. — Fay  lathe. 


TURNING  AND  BORING 


183 


length  but  of  comparatively  small  diameter,  the  two  machines 
thus  mutually  supplementing  each  other. 
As  in  other  automatic  lathes  the  operations  of  the  cutting 


FIG.  162. — Examples  of  work  for  which  the  Fay  lathe  is  adapted. 

tools  of  the  Fay  lathe  are  controlled  by  cams,  a  cam  drum, 
carrying  cams  upon  both  its  interior  and  exterior  surfaces, 
being  located  at  the  head-stock  end  of  the  machine.  The  turn- 


FIG.  163.— Lo-swing  lathe. 

ing-tool  carriage  is  mounted  upon  a  sliding  bar  which  is  drawn 
endwise  for  the  feed  by  a  cam  on  the  interior  of  the  drum. 


184 


METHODS  OF  MACHINE  SHOP  WORK 


The  rear  of  the  tool  carriage  rests  upon  a  support  which  may 
be  inclined  to  the  horizontal  or  be  curved  if  desired  and  thus 
produce  both  tapered  and  curved  outlines.  In  the  rear  is  a 
second  tool  support  mounted,  as  shown  in  Fig.  161,  on  an 
arm  also  carried  on  a  sliding  and  turning  bar.  This  tool 
support  is  most  used  for  facing  cuts  for  which  it  is  actuated  by 
a  heart-shaped  cam  within  the  bed.  It  may  also  be  used  for 
turning  if  desired.  Each  tool  support  may  carry  several  tools  if 
the  work  calls  for  them.  The  character  of  the  work  to  which 


Motor.  Shaft  28s"iong  45%  Carbon 

Steel 
Turning  Time,  Ready  for  Grinding 

l&  Minutes 


FIG.  164. — Examples  of  work  to  which  the  Lo-swing  lathe  is  adapted. 

the  lathe  is  adapted  and  the  method  of  holding  the  cutting  tools 
are  indicated  in  Fig.  162. 1 

The  Lo-swing  lathe,  Fig.  163,  is  a  single  purpose  machine 
intended  for  doing  work  on  bar  stock  of  the  class  that  must  be 
done  between  centers  and  nothing  else.  The  swing  is  reduced 
to  that  necessary  for  work  of  three  and  one-half  inches  diameter. 
It  has  no  part  corresponding  to  a  turret  but  the  essential  feature 
of  the  turret,  the  use  of  several  tools,  and  the  preservation  of 
the  adjustment  of  the  tools  is  retained.  Two  tool  carriages, 

1  Reproduced  from  Machinery. 


TURNING  AND  BORING 


185 


each  capable  of  holding  several  tools,  are  provided,  so  arranged 
as  to  pass  by  the  tail  stock  for  starting  the  cuts  and  for  short 
work.  The  general  character  of  the  work  for  which  the  lathe 
is  adapted,  together  with  the  manner  in  which  the  successive 
tools  act,  is  shown  in  Fig.  164.  This  illustration  does  not, 
however,  show  the  operations  of  thread  cutting  nor  taper 
turning  for  both  of  which  the  machine  is  equipped. 

THE  BORING  BAR 

For  a  great  variety  of  purposes  holes  must  be  bored  in  pieces 
of  a  size  and  character  such  that  no  modification  of  the  lathe 


FIG.  165. — Large  boring  bar  at  work. 

can  accommodate  them.     Such  holes  are  bored  by  means  of 
boring  bars1  which  are  of  three  kinds:  (a)  those  which  are  fed 

1  The  boring  bar  was  invented  in  1774  by  John  Wilkinson  for  use  in  the  boring 
of  steam-engine  cylinders  for  James  Watt  which,  at  the  beginning,  was  the  most 
troublesome  and  difficult  construction  problem  with  which  Watt  had  to  deal. 
The  boring  bar  was  of  the  traveling-head  variety  and  it  was  the  first  machine 
tool  to  approximate  modern  standards. 


186 


METHODS  OF  MACHINE  SHOP  WORK 


through  bearings  with  the  cut,  the  tool  being  fixed  in  the  bar; 
(b)  those  which  are  stationary  as  regards  endwise  motion  and 
have  tools  fixed  to  them,  the  work  traveling  lengthwise  of  the 
bar;  (c)  those  in  which  both  work  and  bar  are  fixed  as  regards 
endwise  motion,  the  tool  being  mounted  in  a  traveling  head 
which  is  fed  lengthwise  of  the  bar  by  means  of  a  screw. 

An  application  of  a  bar  of  the  traveling-head  variety  is  shown 
in  Fig.  165  from  the  Westinghouse  Machine  Company,  the  work 
in  progress  being  the  boring  of  the  seats  for  the  bearing  shells 
of  a  large  upright  vertical  engine.  The  bar  is  supported  in 


FIG.  1 66. — Boring  bar  for  taper  holes. 


bearings,  one  of  which  is  bolted  to  one  end  of  the  casting  and 
the  others  to  cross  beams  «as  clearly  shown,  the  drive  being 
through  a  worm  gear  and  an  electric  motor  belted  to  the  worm 
shaft.  Such  bars  and  their  attachments  naturally  take  a  great 
variety  of  forms  in  accordance  with  the  necessities  of  individual 
cases. 

A  boring  bar  for  taper  holes,  from  the  works  of  the  Niles- 
Bement-Pond  Company,  is  shown  in  Fig.  166.  The  bar  is 
swiveled  to  its  supports  and  one  end  may  be  offset  to  any 
angle  required. 

BORING  AND  TURNING  SPHERICAL  SEAT 

The  growing  use  of  the  self-aligning  ball-and-socket  con- 
struction for  large  bearings  necessitates  the  provision  of  suitable 
means  for  machining  the  spherical  seats — external  in  the  case  of 


TURNING  AND  BORING 


187 


FIG.   167. — Turning  spherical  seats  for  bearings. 


FIG.  1 68. — Boring  spherical  seats  for  bearings. 


188  METHODS  OF  MACHINE  SHOP  WORK 


FIGS.   169  and  170. — Boring  bar  for  spherical  seats. 


TURNING  AND  BORING  189 

the  bearing  shells  and  internal  in  the  case  of  their  supports. 
Fig.  167  from  the  works  of  the  Westinghouse  Machine  Company 
shows  such  a  provision  for  the  turning  of  the  spherical  seat  on 
a  large  bearing  shell.  The  provision  required  is  that  the  cut- 
ting tool,  instead  of  traveling  in  a  straight  line  as  in  the  ordinary 
lathe,  shall  swing  on  the  arc  of  a  circle,  the  center  of  which  is 
vertically  below  the  center  line  of  the  lathe.  The  means  by 
which  this  is  obtained  are  sufficiently  obvious  from  the 
illustration. 

Figs.  168-170,  from  the  same  source  as  the  last,  show  a 
superior  equipment  for  boring  large  spherical  seats.  Fig.  168 
shows  the  equipment  in  position  boring  the  seat  of  the  main 
bearing  of  a  large  horizontal  engine.  The  boring  bar  and  its 
driving  mechanism  are  suspended  from  a  frame  which  is  bolted 
to  the  top  of  the  bearing  jaws.  Figs  169  and  170  show  the 
outfit  turned  up  on  its  side  and  from  opposite  ends,  the  frame 
casting  being  in  the  background.  The  bar  carries  three  tool 
heads  of  which  the  outer  ones,  which  travel  on  the  bar  for  the 
feed,  bore  the  cylindrical  ends  of  the  engine  casting.  The  inner 
head  swivels  on  the  bar  and  is  shown  connected  by  links  to 
one  of  the  traveling  heads.  The  boring  of  the  cylindrical  ends 
having  been  accomplished  with  the  links  removed,  the  cutting 
tools  are  removed  from  the  end  heads  and  inserted  in  the  swivel 
head.  The  links  being  then  placed  in  position  the  result  of 
feeding  the  end  head  along  the  bar  is  to  traverse  the  cutting  tool 
on  the  swivel  head  in  the  arc  of  a  circle  and  bore  the  spherical 
seat.  The  feed  screw  by  which  the  traverse  is  accomplished 
is  shown  above  the  bar  in  both  Figs.  169  and  170. 

CYLINDER  BORING  MACHINES 

When  boring  cylinders  for  vertical  steam  engines  of  large 
size,  the  best  practice  requires  that  they  be  bored  in  a  vertical 
position  in  order  to  avoid  the  distortion  due  to  their  own  weight 
and  Fig.  171  shows  a  machine  for  boring  such  cylinders  at  the 
Brooklyn  Navy  Yard.  The  boring  bars,  of  which  three  appear 
at  the  left  of  the  machine,  are  of  the  traveling-head  variety  and, 
when  at  work,  are  supported  above  and  below  by  the  bearings 


190 


METHODS  OF  MACHINE  SHOP  WORK 


plainly  shown.  The  driving  of  the  bar  is  from  above  by  means  of 
gearing.  In  the  foreground  is  a  facing  head  for  facing  the 
flanges  of  the  cylinders.  When  mounted  upon  the  bar  its  arm 


FIG.  171. — Large  vertical  cylinder  boring  machine  and  boring  bars. 

projects   radially   and   the   tool   slide   with  which  it  is  fitted 
travels  radially  and  performs  the  required  operation. 


CHAPTER  IX 

FLOOR-PLATE  WORK 

The  floor-plate  system  of  machine  tools — Such  tools  have  no  defined 
limit  of  capacity— Uses  of  the  various  tools — The  floor-plate  boring 
mill. 

CHARACTERISTICS  OF  FLOOR-PLATE  TOOLS 

All  of  the  machine  tools  elsewhere  shown  have  in  common  the 
feature  that  the  size  of  the  work  which  they  can  normally  take 
in  is  limited  by  the  dimensions  of  the  machine.  Numerous 
ingenious  expedients  enable  work  to  be  done  of  dimensions 
which  exceed  those  for  which  the  machines  were  designed,  but 
they  are  but  makeshifts  at  best,  and  the  growing  frequency 
with  which  large  work  is  required  has  led  to  the  construction  of 
machines  of  an  entirely  different  type  in  which  there  is  no 
designed  limit  of  capacity.  With  these  machines  the  limit  to 
the  size  of  parts  is  no  longer  set  by  the  character  of  the  machine- 
shop  equipment  but  by  the  facilities  of  the  railroad  companies 
for  transporting  the  pieces,  the  limiting  dimensions  being 
reached  with  the  largest  pieces  that  will  pass  through  railroad 
tunnels  and  bridges. 

This  system  of  machine  tools,  known  as  floor-plate  tools,  is 
due  to  John  Riddell,  mechanical  superintendent  of  the  Schenec- 
tady  works  of  the  General  Electric  Company,  from  which 
works  the  system  has  spread  to  others  doing  large  work. 

The  starting  point  of  the  system  is  the  provision  of  a  heavy 
cast-iron  floor  plate  made  in  sections,  usually  ten  feet  square, 
and  fitted  with  T  slots  by  which  both  work  and  tools  are  bolted 
down.  Large  floor  areas  are  fitted  with  these  plates,  a  section 
of  such  a  floor  at  the  General  Electric  Company's  Schenectady 
works  being  shown  in  Fig.  172.  The  machine  tools  themselves 
are  of  considerable  variety,  several  being  shown  in  Figs.  173 
-176,  from  which  it  will  be  apparent  that  it  is  the  individual 

191 


192 


METHODS  OF  MACHINE  SHOP  WORK 


FIG.  172. — Modern  floor  plate. 


FIG.  173. — Portable  floor  plate  drilling  machine. 


FLOOR-PLATE  WORK 


193 


oj 

•E 


fcO 

•3 
I 


13 


194 


METHODS  OF  MACHINE  SHOP  WORK 


electric  motor  drive  that  has  made  the  system  feasible.  Each 
machine  is  provided  with  its  own  motor,  convenient  plugs  being 
provided  for  connecting  at  any  convenient  point.  In  each 
case  also  the  machine  is  provided  with  a  suitable  lifting  bale 
by  which  the  overhead  crane  may  transport  it  from  place  to 
place. 


FIG    176. — Portable  floor  plate  milling  machine. 

EXAMPLES  OF  FLOOR-PLATE  TOOLS 

Fig.  174  shows  two  portable  Newton  slotting  machines  at 
work  planing  the  feed  of  a  motor  frame.  Fig.  175  shows  a  hori- 
zontaf  spindle  Newton  drilling  machine  mounted  on  an  adjust- 


FLOOR-PLATE  WORK 


195 


able  base  and  Fig.  173  a  drilling  machine  of  somewhat  different 
pattern,  though  by  the  same  maker,  engaged  on  a  much  larger 
piece  of  work.  In  both  cases  the  piece  of  work  is  mounted  on  a 
central  turn  table.  This  last  machine  is  also  provided  with  a 
vertical  feed  to  the  spindle  head  and  Fig.  176  shows  it  at  work 
milling  the  dove-tail  slots  in  an  armature  spider.  The  floor- 
plate  system  as  applied  to  heavy  milling  operations  is  shown  in 


FIG.  177. — Section  and  half  section  of  floor  plate  boring  mill. 

Figs.  240-242  and  as  applied  to  the  cutting  of  large  gears  in 
Fig.  270. 

THE  FLOOR-PLATE  BORING  MILL 

One  of  the  applications  of  this  system  is  to  the  floor-plate 
boring  mill.  The  boring  mill,  like  all  machine  tools  other 
than  floor-plate  tools,  is  limited  in  the  capacity  of  the  work  which 
it  will  take  in,  whereas  the  floor-plate  boring  mill,  like  other 


196 


METHODS  OF  MACHINE  SHOP  WORK 


floor-plate  tools,  has  no  such  limitation.  The  floor-plate  boring 
mill  consists  of  a  revolving  table  sunk  in  the  regular  floor  plate 
which  surrounds  it,  the  work  and  the  machine  tools  being 
mounted  upon  the  revolving  and  the  stationary  plates  in  various 
ways  and  in  accordance  with  the  requirements  of  the  piece  of 
work  in  hand. 

A  section  and  half  section  of  such  a  floor-plate  mill  at  the  works 
of  the  Crocker- Wheeler  Company  is  shown  in  Fig.  177.  The 
revolving  table  is  shown  at  a,  the  center  piece  b  being  stationary 


FIG.  178. — The   tool  revolves  while  the  work  stands  still. 
Work  of  the  floor-plate  boring  mill. 

and  serving  as  a  bearing  for  the  revolving  table.  A  supple- 
mentary, non-revolving,  removable  piece  c  is  provided,  properly 
fitted  at  its  center  so  that  it  may  be  quickly  dropped  into  place 
concentrically  with  the  other  parts.  This  supplementary  piece 
is  only  occasionally  used  but  it  adds  materially  to  the  flexibility 
of  the  machine.1 

In  use,  the  work  is  sometimes  bolted  to  the  surrounding  floor 
plate,  the  tool  being  mounted  upon  and  turning  with  the  re- 

1  The  heavy  lines  of  the  upper  view  show  oil  supply  and  drain  pipes. 


FLOOR-PLATE  WORK 


FIG.  179. — The  work  revolves  while  the  tool  stands  still. 


I 


L 


FIG.  1 80. — The  work  revolves  while  the  tool  stands  still. 
Work  of  the  floor-plate  boring  mill. 


198  METHODS  OF  MACHINE  SHOP  WORK 

volving  table,  while  in  other  cases  the  reverse  arrangement  is 
used,  the  arrangement  being  determined  by  the  size  of  the  work. 
Fig.  178  shows  a  generator  ring  frame  mounted  upon  the  sur- 
rounding plate  and  the  tool  mounted  upon  the  revolving  plate, 
other  tools  performing  additional  operations  simultaneously. 
Fig.  179  shows  the  reverse  arrangement,  the  work  being  here 
mounted  on  the  revolving  table  while  the  tool  support  is 
mounted  on  the  surrounding  floor  plate.  For  still  smaller  work 
as  in  Fig.  180,  the  tool  is  mounted  upon  the  inner  supplemen- 
tary plate,  which  does  not  revolve,  while  the  ring  frame  is 
mounted  upon  the  revolving  table  and,  obviously,  if  re- 
quired, the  reverse  arrangement  may  be  used,  the  work  being 
mounted  upon  the  supplementary  plate  and  the  tool  upon  the 
revolving  table. 


CHAPTER  X 

DRILLING 

Types  of  drilling  machines — Jigs  and  their  uses — Gang,  multiple- 
spindle  and  station  drilling  machines — The  laying-out  machine  for  the 
accurate  spacing  of  holes — The  base  line  system  of  drawings — Other 
methods  of  spacing  holes — The  master  plate. 

TYPES  OF  DRILLING  MACHINES 

The  drilling  machine  is  made  in  a  great  variety  of  forms,  of 
which  three  by  the  Cincinnati  Bickford  Tool  Company  are 
shown  in  Figs.  181-183.  The  most  common  form,  called  the 
upright  drilling  machine,  with  modern  and  unusual  features,  is 
shown  in  Fig.  181.  With  the  two  that  follow,  it  is  fitted  with 
the  popular  constant -speed  pulley  drive.1  By  means  of  the 
two  bevel  gears  on  the  upper  end  of  the  spindle  and  their  con- 
nections, the  spindle  may  be  revolved  in  either  direction  and 
with  the  back  gears  and  the  convenient  lever  for  manipulating 
them  the  speed  may  be  quickly  changed.  Thus  equipped  the 
machine  may  be  used  for  tapping  as  well  as  drilling.  The  tap 
having  been  driven  through  the  work,  movement  of  the  front 
lever  depending  from  the  driving  head  reverses  the  tap,  when 
movement  of  the  rear  lever  accelerates  the  speed  of  withdrawal. 
A  depth  gage  for  the  depth  of  drilling  and  an  automatic  trip 
whereby  the  feed  is  automatically  stopped  when  the  desired 
depth  has  been  reached  are  also  provided. 

To  accommodate  work  in  which  holes  must  be  drilled  at  a 
considerable  distance  from  their  sides  the  radial  drill,  Figs. 
182  and  183,  has  large  application.  In  most  cases  these 
machines  are  made  as  shown  in  Fig.  182,  the  drill  spindle  being 
always  vertical.  Such  machines  are  called  plain  radials.  In 

1  To  the  best  of  the  author's  knowledge,  the  first  machine  tool  of  any  kind  to 
be  thus  driven  was  a  Bickford  drilling  machine  exhibited  at  the  Pan-American 
Exposition  of  1900. 

199 


200 


METHODS  OF  MACHINE  SHOP  WORK 


other  cases  as  in  Fig.  183  the  arm  is  so  made  as  to  swivel  about 
a  horizontal  line  and  the  drill  spindle  about  its  vertical  center 
line,  whereby  the  spindle  may  be  made  to  perform  its  function 


FIG.  181. — Upright  drilling  and  tapping  machine. 

at  any  angle  with  the  horizontal  and  vertical  planes.  Such 
machines  are  called  universal  radials.  Sometimes  one  of  these 
adjustments  is  omitted  and  the  machine  becomes  a  semi- 


DRILLING 


201 


FIGS.  182  and  183. — Plain  and  universal  radial  drilling  machines. 


202 


METHODS  OF  MACHINE  SHOP  WORK 


universal  radial.  The  convenience  of  the  universal  and  semi- 
universal  machines  adapts  them  to  the  performing  of  otherwise 
difficult  operations,  but  the  necessary  joint  at  the  base  of  the 
arm — precisely  the  point  where  stiffness  is  most  needed — robs 
them  of  stiffness  and,  except  as  regards  this  convenience  of 
adjustment,  which  is  only  occasionally  required,  the  plain 
radial  is  much  to  be  preferred. 

DRILLING  JIGS 

Drilling   in    connection    with    manufacturing   operations   is 
always  done  in  connection  with  drilling  jigs  which  take  a  great 


FIG.  184. — Various  forms  of  drilling  jigs. 

variety  of  forms,  a  few  of  which  are  shown  in  Fig.  184.  The 
object  of  a  drill  jig  is  to  guide  the  tool,  the  laying-out  of  the 
holes  being  done  once  for  all  on  the  jig,  uniformity  of  spacing 


DRILLING 


203 


in  the  work  being  thus  assured.  To  insure  permanence  of  the 
locations  the  holes  are  bushed  with  hardened  steel  bushes. 
Eventually  even  hardened  bushes  wear,  but  it  is  then  a  simple 
matter  to  remove  the  old  and  insert  new  bushes,  the  result 
being  to  restore  the  jigs  to  their  original  accuracy. 

This  word  jig  is  properly  applied  to  appliances  which  guide 
cutting  tools.     Numerous  other  appliances  used  in  connection 


FIG.  185. — Large  boring  bar  jig. 

with  other  operations  which  locate  the  work,  rather  than  guide 
the  tool,  are  frequently  called  jigs  but  are  more  properly 
fixtures. 

Jigs  for  large  work  are  frequently  seen,  such  an  one  from  the 
Cincinnati  Planer  Company  being  shown  in  Fig.  185,  which 
illustrates  a  jig  for  the  bearings  of  the  various  shafts  which 
extend  through  a  planer  bed.  These  bearings  it  serves  to  locate 
in  proper  position  with  respect  to  one  another  and  also  with 
respect  to  the  V's  of  the  planer.  The  jig  has  locating  V's 


204  METHODS  OF  MACHINE  SHOP  WORK 

which  enter  the  V's  of  the  planer  bed.  The  tool  guided  by  the 
jig  is  a  boring  bar  which  is  guided  at  both  ends  by  bushes  in 
the  jig  body,  the  drive  being  from  a  radial  drilling  machine 
through  an  adjustable  knuckle  joint. 

GANG  AND  STATION  DRILLING  MACHINES 

Drilling  machines  are  frequently  arranged  in  gangs,  of  which 
an  example  by  the  W.  F.  and  John  Barnes  Company  is  shown 


FIG.  1 86. — Gang  drilling  machine. 

in  Fig.  1 86.  With  a  piece  of  work  in  position  the  operator 
has  but  to  trip  a  lever  when  the  drill  drops  to  the  work,  feeds 
through  it  and,  when  the  hole  is  finished,  automatically  flies 
back  to  the  starting  point.  The  spindles  are  fitted  in  succession 
with  various  drills  and  reamers,  the  work  being  shifted  from 
spindle  to  spindle  and  the  four  tools  operating  simultaneously  on 
as  many  pieces.  Arranged  in  this  manner  the  equipment  be- 
comes essentially  a  station  machine  in  which  the  shifting  from 
station  to  station  is  by  hand. 


DRILLING  205 

An  automatic  station  drilling  machine  by  the  Windsor 
Machine  Company  is  shown  in  Fig.  187.  The  work  is  carried 
on  a  turn  table  fitted  with  as  many  chucks  as  there  are  drilling 
spindles  plus  one,  an  extra  station  being  required  for  loading 
and  unloading  the  chucks.  The  feed  is  effected  by  the  vertical 
movement  of  the  turn  table  which  revolves  one  step  after  the 
completion  of  each  drilling  operation.  Each  piece  of  work  is 
finished  as  it  passes  the  last  operative  station  from  which  the 
next  indexing  movement  carries  it  to  the  idle  or  loading  station 
where  the  finished  piece  is  removed  and  a  new  one  is  substituted, 
with  a  drilling  operation  in  progress.  The  spindles  are  driven 
by  universally  adjustable  telescopic  connections  permitting 
lateral  adjustment  of  the  cutting  tool  to  any  point  on  the  face 
of  the  work  and  change  gears  are  provided  by  which  the  speeds  of 
the  different  spindles  may  be  independently  adjusted.  Other 
operations  than  drilling,  such  as  reaming,  counterboring,  etc., 
suitable  for  revolving  tools  may  be  carried  on.1 

MULTIPLE-SPINDLE  DRILLING  MACHINES 

A  comparatively  recent  development  of  the  drilling  machine  is 
the  multiple-spindle  machine,  if  which  an  example,  by  the 
Baush  Machine  Tool  Company,  is  shown  in  Fig.  188.  The 
drills  are  driven  from  the  central  spindle  by  gearing  and  uni- 
versal telescopic  joints  and  are  adjustable  in  number  and  to 
cover  any  layout  within  the  limits  of  the  machine. 

Small  multiple-spindle  drill  heads  are  frequently  made  for 
attachment  to  otherwise  plain  machines — such  attachment 
being  frequently  homemade  for  the  work  in  hand.  Two  such 
cases  from  the  works  of  the  General  Electric  Company  are  shown 
in  Fig.  189  together  with  the  jigs  which  go  with  them.  The 
various  spindles  are  driven  by  suitable  gears,  all  connected  to  a 
central  gear  attached  to  the  main  spindle  at  the  center. 
Other  cases  of  multiple-spindle  drill  heads  by  the  Langelier 
Manufacturing  Company  are  shown  in  Figs.  190-192.  Each 
of  these  is  designed  for  a  special  piece  of  work  and  different 
heads  are  made  to  interchange  on  the  same  drilling  machine. 

1  The  reader  should  compare  this  illustration  with  Fig.  159  showing  a  station 
machine  in  which  the  work  revolves. 


206 


METHODS  OF  MACHINE  SHOP  WORK 


•c 


P 


DRILLING 


207 


The  driving  of  the  spindles  is  by  the  mechanism  shown  in  Fig. 
193.  Each  spindle  carries  above  its  bearing  an  offset  crank, 
the  spindles  being  driven  in  common  by  a  crank  plate 


FIG.  189. — Multiple  spindle  drill  heads. 

mounted  eccentrically  in  the  main  spindle.  This  construction 
permits  the  spindles  to  be  grouped  together  more  closely  than 
any  other,  the  limiting  center  distance  being  two  diameters  of 
the  drill. 


208 


METHODS  OF  MACHINE  SHOP  WORK 


1.1 


DRILLING 


209 


FIG.   193. — Method  of  driving  multiple  spindle  drill  heads. 


14 


FIG.  194. — An  example  of  highly  organized  multiple  spindle  drilling. 


210  METHODS  OF  MACHINE  SHOP  WORK 

A  highly  organized  piece  of  multiple-spindle  drilling  from 
the  works  of  the  Westinghouse  Electric  and  Manufacturing 
Company  is  shown  in  Fig.  194.  The  work  in  progress  is  the 
drilling  of  one  side  of  a  shell  of  an  electric  railway  motor.  The 
scheme  is  to  provide  two  jigs,  one  of  which  is  loaded  with  work 
while  the  other  is  under  the  drilling  machine  in  action,  and  then, 
in  addition  to  this,  to  provide  means  for  the  quick  interchange 
of  the  two  jigs.  A  suitable  track  and  turntable  will  be  seen,  a 
short  piece  of  track,  not  seen,  extending  underneath  the  drilling 
machine  and  at  right  angles  to  the  track  shown.  The  jigs  are 
fitted  with  wheels  suitably  flanged  for  the  track.  From  a  pile 
of  undrilled  castings  in  the  foreground  the  operator  loads  the 
jig,  provisions  for  doing  which  quickly  are  provided  as  shown. 
Meanwhile  a  preceding  casting  has  been  drilled  under  the 
machine.  When  finished  it  is  run  out  on  the  turntable  which  is 
turned  through  ninety  degrees  and  the  jig  and  its  work  are 
run  off  to  the  rear  where  the  jig  is  unloaded.  The  previously 
loaded  jig  is  then  run  on  the  turntable  and  under  the  machine, 
when  the  other  jig  is  run  back  to  the  loading  position  and  loaded, 
this  sequence  of  operations  going  on  indefinitely. 

LAYING  OUT  MACHINES  FOR  SPACING  HOLES 

The  accurate  laying  out  of  holes  in  jigs  is  a  subject  on  which  a 
book  could  be  written.  It  is,  perhaps,  the  master  operation  of 
the  tool  room  and  a  great  many  methods  of  doing  it  have  been 
devised. 

A  superior  method  of  doing  this  is  by  the  use  of  a  special 
machine,  for  this  purpose  only,  from  the  works  of  the  Burrough's 
Adding  Machine  Company,  shown  in  Fig.  195.  The  machine  is 
by  the  Sigourney  Tool  Company  from  designs  by  the  Burrough's 
Company.  The  work  table  is  arranged  similarly  to  that  of  a 
knee-type  milling  machine  with  the  addition  that  it  has  fitted 
to  the  work  table,  in  such  positions  as  to  read  in  two  directions 
at  right  angles  from  one  another,  two  finely  graduated  scales 
which  are  provided  with  verniers.  With  this  construction  the 
adjustment  of  the  table  may  be  made  with  great  accuracy  and 
convenience,  the  convenience  being  increased  by  the  fact  that 
both  scales  and  verniers  are  adjustable  endwise  in  order  that  the 


DRILLING 


211 


212  METHODS  OF  MACHINE  SHOP  WORK 

work  may  be  begun  with  the  first  reading  at  the  zero  or,  more 
frequently,  at  an  even  inch  of  the  scale.  To  prevent  the  side- 
wise  crawling  tendency  of  the  drill  on  the  surface  of  the  work, 
it  is  guided  by  a  bush  inserted  in  an  arm  which  projects  from  the 
machine  frame  and  since,  because  of  the  clearance  with  which 
they  are  provided,  twist  drills  cannot  be  made  to  fit  jig  holes 
with  precision,  the  hole,  after  being  drilled,  is  reamed  with  a 
rose  reamer  having  a  ground  shank  which  accurately  fits  a 
second  bush  in  the  same  arm.  The  machine  is  fitted  with  a 
complete  assortment  of  bushes  and  reamers  which  are  kept  in 
the  cabinet  below  it. 

The  largest  and  finest  example  of  this  method  of  attacking 
the  jig-making  problem  with  which  the  author  is  acquainted  is 
shown  in  Figs.  196-198,  from  the  (British)  firm  Alfred  Herbert, 
Limited.  The  general  principle  of  the  machine  does  not  differ 
from  the  one  just  shown,  although  it  will  be  seen  to  have  much 
greater  capacity,  the  longitudinal  traverse  being  sixty  and  the 
transverse  traverse  thirty  inches.  The  method  of  measuring 
the  distances  between  holes  is,  however,  entirely  different  and 
capable  of  much  greater  accuracy,  being  based  on  the  use  of 
end  measure  rods,  micrometer  screws  and  gravity  drop  pieces, 
these  last  being  similar  to  the  drop  piece  described  in  connec- 
tion with  the  Pratt  and  Whitney  measuring  machine.  These 
features  are  used  for  the  fine  adjustment  only.  While  the 
traverse  screws  are  not  depended  upon  for  final  settings,  they 
are  fitted  with  graduated  dials  for  the  coarse  adjustments  and, 
to  save  the  counting  of  their  revolutions,  graduated  scales  are 
provided  for  both  longitudinal  and  transverse  movements. 

Referring  to  Fig.  197,  the  pilot  wheel  by  which  the  transverse 
adjusting  screw  is  manipulated  is  plainly  seen.  Beyond  it, 
near  the  base,  is  its  graduated  dial,  beyond  which,  on  the  bed,  is 
the  scale.  In  the  foreground  is  the  micrometer  dial  and  in 
front  of  it  the  gravity  drop  piece,  while  beyond  it  on  the  base 
is  the  end-measure  rod.  The  corresponding  parts  for  the 
longitudinal  adjustment  are  shown  in  Fig.  198.  As  the  moving 
parts  are  heavy  a  more  sensitive  adjustment  than  that  of  the 
pilot  wheels  is  necessary,  the  provision  for  this  being  most 
clearly  shown  in  Fig.  197.  It  consists  of  a  lever  which,  while 


DRILLING 


213 


FIGS.  197  and  198. — Details  of  large  tool  room  laying  out  machine. 


214  METHODS  OF  MACHINE  SHOP  WORK 

usually  free  from,  may  be  clamped  to  the  traverse  screw.  The 
lever  is  provided  with  an  adjusting  screw  at  its  end  which  bears 
on  a  fixed  abutment.  With  the  lever  clamped  to  the  main 
screw,  the  adjusting  screw  will  obviously  give  very  fine 
adjustments. 

The  table  feed  and  adjusting  screws  of  high-class  milling 
machines  are  made  to  a  high  degree  of  precision  and  are  fitted 
with  micrometer  dials  whereby  readings  to  thousandths  are 
obtained.  With  the  work  clamped  to  the  work  table  and  a 
boring  tool  placed  in  the  spindle,  the  lengthwise,  transverse  and 
elevating  screws  provide  means  for  measuring  the  spaces  be- 
tween holes  in  a  manner  analogous  to  those  used  with  these 
laying-out  machines.  This  plan  is  often  used  but  is  not  to  be 
recommended  unless  the  milling  machine  is  new.  Accurate 
screws  are  provided  in  these  machines  because  customers 
expect  them  and  not  because  it  is  a  suitable  place  for  such 
screws,  for  it  is  not.  Their  use  as  feed  screws  under  the  pressure 
due  to  the  cut  leads  to  wear  which  is  greatest  where  the  screws 
are  most  used,  that  is  near  their  centers  of  length.  Conse- 
quently, whatever  their  accuracy  when  new  they  do  not  long 
retain  it. 

The  appropriate  construction  would  embody  the  division  of 
functions  which  appears  in  these  laying-out  machines,  in 
both  of  which  the  moving  of  the  parts  and  the  measurement  of 
the  movements  are  entirely  distinct  and  hence  wear  of  the  screws 
has  no  effect  on  the  accuracy  of  the  readings.  The  Herbert 
machine  is  unnecessarily  refined  for  commercial  milling  ma- 
chines but  there  seems  to  be  no  reason  why  the  Burroughs  con- 
struction is  not  applicable  to  such  machines. 

BASE  LINE  DRAWINGS 

Drawings  for  work  to  be  made  on  machines  of  this  type  are 
laid  out  on  the  base  line  plan.  Were  the  dimensions  between 
holes  given  as  is  common  on  construction  drawings,  the  practice 
would  necessitate  a  large  amount  of  addition  and  subtraction 
of  fractional  dimensions  in  order  to  obtain  the  readings  of  the 
scales,  a  process  which  would  not  only  consume  time  but  would 
be  productive  of  errors.  These  objections  are  overcome  by  the 


DRILLING 


215 


base  line  drawings  in  which  the  locations  of  all  the  holes  are 
laid  out  as  coordinates  from  base  lines.  An  example  of  this 
kind  of  drawing  is  shown  in  Fig.  199.  The  locations  of  the 
holes  are  always  the  true  readings  of  the  scales  so  far  as  the 
fractions  are  concerned,  although  the  whole  inches  frequently 
differ  in  accordance  with  the  location  of  the  zeros  of  the  scales. 
In  some  cases  the  base  lines  are  external  to  the  piece  of  work 
while  in  others,  as  in  the  present  case,  the  base  lines  pass  through 


K 0.620s--* 

\*- 0.544  "---;-> 

I     K- 0525 -* 

I    \\f- 0.5225^--- -f 
(<-  -Q38/3 ^ 


Tirz§_i    i  «w  u  • 

—  4-  -F- — e — '-e-  •  . 


iQli^ili^—^ 
a  » '  i  !  •    1 1  *-**-•*=*- -=---= 


FIG.  199. — Base  line  drawing  for  use  with  laying  out  machines. 

the  center  of  one  of  the  principal  holes.  This  hole  being  made 
first  and  the  scale  and  vernier  adjusted  to  read  zero  or  an  even 
inch,  the  locating  of  the  other  holes  becomes  a  simple  matter. 

OTHER  METHODS  OF  SPACING  HOLES 

These  machines  provide  the  most  obvious  and  the  quickest 
method  of  locating  holes  with  accuracy  and  their  cost  would  be 
justified  in  a  large  number  of  shops.  Nevertheless  they  are 


216 


METHODS  OF  MACHINE  SHOP  WORK 


seldom  found  and  other  methods,  of  which  many  have  been 
developed  by  the  tool  makers,  must  be  resorted  to.  An  ex- 
tremely accurate  and  satisfactory  method  has  already  been 
shown  in  connection  with  the  Johansson  gages,  Fig.  106,  and  the 
same  plan  is  obviously  applicable  and  is  frequently  used  with 
plug  and  other  forms  of  gages  as  indicated  in  Fig.  200,  in  which 
the  discs  are  of  such  diameters  as  to  shift  the  piece  of  work  by 
such  amounts  as  will  bring  the  centers  of  the  desired  holes  in 


3 

GOO 

C  )                 tJ 

1 

000 
0 

3 

C)  C) 

FIG.   200. — Gage  method  of  accurately  spacing  holes. 

line  with  the  lathe  spindle.  In  these  cases,  as,  indeed,  in  most 
others,  the  holes  are  finished  with  a  single  pointed  lathe  boring 
tool  which  assures  perfect  alignment  of  the  holes  with  the  lathe 
spindle.  By  this  plan,  the  work  being  swung  in  the  lathe, 
the  size  of  the  pieces  which  can  be  treated  is  limited  by  the 
capacity  of  the  lathe. 

A  method  which,  for  the  highest  class  of  work,  has,  perhaps, 
found  larger  use  than  any  other,  is  the  New  England  button 


DRILLING 


217 


method  which,  while  slow,  is  capable  of  results  of  the  highest 
degree  of  accuracy.  This  method  is  shown  in  Figs.  201-203. 
The  process  involves  the  preliminary  positioning  of  a  series 
of  buttons  at  the  exact  locations  where  the  jig  holes  are  required. 
The  buttons  are  small  cylinders  of  hardened  steel  of  exactly 
the  same  diameter  with  holes  through  them  endwise  and  with 
them  go  small  cap  screws  of  a  diameter  somewhat  less  than 
that  of  the  holes  through  the  buttons. 

The  jig  having  been  planed,  the  tool  maker  lays  out  the  holes 
as  accurately  as  may  be  with  scale  and  dividers  and  drills  and 
taps  holes  for  the  button  holding  cap  screws.  The  buttons  are 
then  lightly  secured  in  their  approxmate  positions  as  shown  in 


3 

'Jig 

Cen  ter  of  Spindle 
^-Button 


FIG.  203. 


Ite 


Jig-' 


FIG.  202. 

The  button  method  of  spacing  holes. 


Fig.  201  and,  using  a  parallel  strip  and  micrometer  as  in  Fig.  202, 
they  are  adjusted  to  the  exact  position  desired.  The  jig  is 
then  strapped  to  a  lathe  face  plate  as  in  Fig.  203  and  carefully 
positioned  until  the  tool  maker's  indicator  stands  still  as  the 
lathe  revolves,  showing  the  button  to  be  exactly  in  line  with  the 
lathe  spindle.  The  button  is  then  removed  and  the  hole  is 
enlarged  to  the  required  size  by  a  boring  tool  held  in  the  tool 
post.  The  jig  is  then  shifted  on  the  face  plate  to  bring  the 
other  buttons  successively  in  line  with  the  spindle  when,  the 
holes  being  bored,  they  are  obviously  accurately  spaced. 


218 


METHODS  OF  MACHINE  SHOP  WORK 


As  with  the  gage  method  the  pieces  which  can  be  handled  in 
this  way  are  limited  in  size  by  the  capacity  of  the  lathe  and  in 
such  cases  the  button  method  may  be  applied  to  the  milling 
machine  as  indicated  in  Fig.  204.  The  indicator  is  here  mounted 
in  the  spindle  of  the  milling  machine  and  the  jig  plate  is 


FIG.  204. — Use  of  the  button  method  on  milling  machines. 

adjusted  by  means  of  the  milling  machine  table  screws  until 
the  indicator  index  stands  still  when  the  spindle  is  revolved. 
This  button  is  then  removed,  a  boring  tool  is  substituted  for 
the  indicator  and  the  hole  is  bored— the  process  being  repeated 
in  succession  for  the  remaining  buttons. 

Twist  drills  cannot  be  depended  upon  for  making  the  holes, 


DRILLING 


219 


because  milling  machines  have  no  provision  for  preventing 
their  crawling  sidewise,  which  they  have  a  tendency  to  do.  A 
hole  is  therefore  drilled  somewhat  smaller  than  the  final  size 
and  is  then  enlarged  by  a  boring  tool  constructed  on  the 
principle  of  Fig.  205.  The  action  is  precisely  the  same  as  that 
of  a  lathe  boring  tool  except  that  the  tool,  instead  of  the 
work,  revolves,  and  a  hole  in  true  alignment  with  the  machine 
spindle  is  the  result.  Set  screws  a,  b  serve  to  adjust  the  tool  to 
the  cut. 

Another  method,  commonly  called  the  disc  method,  is  shown 


FIG.   205. — Revolving  boring  tool. 

in  one  application  in  Figs.  206-208.  Holes  are  required  spaced 
as  in  Fig.  206.  It  is  easy  to  calculate  and  to  make  three  discs 
of  diameters  such  that,  located  concentrically  with  the  desired 
holes,  they  will  be  mutually  tangent  to  one  another  as  shown 
in  Fig.  207.  The  discs  are  made  with  a  recess  at  their  centers 
and  are  lightly  secured  to  the  jig  plate,  using  shellac  for  light 
work  and  solder  for  heavier  work.  The  jig  plate  with  the 
attached  discs  is  swung  in  the  lathe  and  adjusted  in  position 
until,  when  the  lathe  spindle  is  turned,  the  center  of  one  of 
the  discs  stands  still  as  shown  by  the  indicator  of  Fig.  208. 
The  disc  is  then  removed  with  a  light  tap  of  the  hammer,  the 
hole  is  bored  as  in  the  button  method  and  the  process  is 


220 


METHODS  OF  MACHINE  SHOP  WORK 


repeated  with  the  other  discs.  This  method  is  modified  accord- 
ing to  circumstances.  Usually  the  holes  are  not  grouped  in 
convenient  sets  of  three  and  in  such  cases  they  can  only  be 
partially  located  by  the  discs.  Cases  of  this  sort  occur  in  con- 
nection with  groups  of  gears.  In  such  a  case  the  diameters  of 
the  discs  are  made  equal  to  the  pitch  diameters  of  the  gears 


Y--- 0.765"-  ->j 


"£        v 


FIG.  206 


FIG.  207. 


.Wood 


•  Sheet  Spring  Steel 


Jo  fit  Too!  Post 


FIG.  208. 
Disc  method  of  accurately  spacing  holes. 

and,  when  placed  in  contact,  they  insure  the  proper  distances 
between  centers,  but,  usually,  the  other  elements  of  their  loca- 
tions must  be  determined  in  some  other  manner. 


THE  MASTER  PLATE 


A  feature  of  jig  work  which  comes  in  as  an  industry  grows  in 
magnitude  is  the  master  plate,  which  is  a  sort  of  reference  gage 
for  the  jig-hole  locations.  The  necessity  for  the  master  plate 


DRILLING 


221 


arises  from  several  causes,  one  of  which  is  the  necessity  for 
duplicate  jigs  in  cases  where  the  required  number  of  parts 
cannot  be  made  with  a  single  jig.  Such  duplicate  jigs  are, 
frequently,  not  made  at  the  same  time — duplicate  and  triplicate 
jigs  being  made  later  than  the  first  one  as  the  necessity  for  them 
arises.  Under  the  master-plate  method  the  careful  laying  out 
of  the  holes  is  done  on  the  plate  once  for  all  and  exact  identity 
of  the  different  jigs  is  insured. 

Another  condition  that  sometimes  makes  the  master  plate 
desirable  will  be  understood  by  considering  the  front  and  back 


r 


Face  Pi 'ate 

MasferP/ate' 

Jig  •  • 


FIG.   209. — Transferring  hole  locations  from  a  master  plate  to  a  jig. 


plates  of  a  clock  or  watch.  Obviously  the  locations  of  the 
bearings  for  the  two  ends  of  the  shafts  must  correspond  and,  both 
being  made  from  the  same  master  plate,  this  is  assured.  The  side 
frames  of  printing  presses  illustrate  the  same  conditions  on  a 
much  larger  scale  and  these  conditions  are  not  infrequent. 

The  master  plate  is  a  simple  flat  plate  of  cast  iron  with  holes 
located  as  in  the  jig  to  which  it  belongs.  Unlike  the  jig  holes, 
however,  those  in  the  master  plate  are  of  a  diameter  having  no 
relation  to  those  in  the  work  and,  moreover,  in  the  same  plate 


222  METHODS  OF  MACHINE  SHOP  WORK 

they  are  all  of  the  same  diameter.     As  they  are  subject  to  but 
little  wear  they  are  frequently  not  bushed. 

With  the  holes  properly  located  in  the  master  plate,  the  boring 
of  the  jig  holes  becomes  a  simple  matter  of  transfer  from  the 
master  plate.  The  method  of  doing  this  is  indicated  in  the 
sketch,  Fig.  209.  A  plug  with  its  shank  turned  to  fit  the  taper 
hole  in  the  lathe  spindle  has  a  projecting  end  of  the  same  diame- 


FIG.  210. — Locating  holes  in  a  master  plate. 

ter  as  the  holes  in  the  master  plate.  The  master  plate  and  jig 
plate  being  dowelled  together,  they  are  mounted  in  the  lathe 
with  the  projecting  end  of  the  plug  entering  one  of  the  holes  in 
the  master  plate.  The  jig  hole  is  then  bored  to  its  required 
size  and  both  plates  are  shifted  to  another  position  on  the  lathe 
face  plate — the  plug  entering  another  hole  in  the  master  plate. 


DRILLING  223 

The  corresponding  jig  hole  is  then  bored  and  so  on  for  the 
others.  As  many  jigs  of  a  kind  as  needed  may  obviously  be 
made  in  this  way  with  positive  uniformity  in  the  locations  of 
their  holes. 

The  locations  of  the  master-plate  holes  may  obviously  be 
determined  by  the  methods  already  shown  for  locating  jig 
holes  when  master  plates  are  not  used.  The  simple  forms  of 
master  plates,  however,  permit  other  methods  to  be  used,  one 
of  which,  from  the  factory  of  the  National  Cash  Register 
Company,  is  shown  in  Fig.  210.  Clamped  to  the  master  plate 
is  a  steel  T  square  which,  however,  differs  from  an  ordinary  T 
square  in  that  the  blade  is  not  attached  to  the  head  but  may  be 
adjusted  lengthwise  of  itself  and  clamped  in  any  location, 
squareness  being  assured  by  a  raised  ledge  on  the  head  against 
which  the  blade  rests.  The  head  of  the  square  carries  a  pin  a 
of  known  diameter  and  at  known  distances  from  the  edges  of  the 
head  and  blade.  The  lower  side  of  the  blade  carries  a  socket  b 
with  a  hole  through  it,  the  center  of  the  hole  being  at  precisely 
the  same  distance  below  the  edge  of  the  blade  as  that  of  the  pin 
a.  A  plug,  not  shown,  is  provided  of  two  diameters,  one  end 
fitting  the  hole  in  the  socket  b  and  the  other  equal  in  diameter 
to  the  pin  a.  With  this  plug  placed  in  the  socket,  the  blade 
may  be  adjusted  by  means  of  a  micrometer  spanning  the  two 
pins  until  the  center  of  the  socket  is  at  the  required  distance 
from  the  pin  a  when  the  blade  is  clamped  to  the  head.  Next 
the  entire  square  is  adjusted  on  the  plate  until  the  center  of  the 
hole  in  the  socket  is  at  the  required  distance  from  the  lower 
edge  of  the  plate — allowance  being  made  in  both  measurements 
for  the  radii  of  the  plugs.  The  square  being  located,  it  is 
clamped  to  the  plate,  the  plug  is  removed  and  replaced  by  a 
bush  suitable  for  guiding  a  drill  which  drills  the  hole.  A 
second  slightly  larger  bush  is  then  substituted  for  the  first  and 
the  hole  is  finished  with  a  rose  reamer  fitting  the  second  bush. 


CHAPTER  XI 
MILLING 

Early  development  of  the  milling  machine — Advantages  of  the  constant- 
speed  drive  as  applied  to  milling  machines — Vertical-spindle  milling 
machines — Types  of  milling  cutters — Uses  of  the  milling  machine — The 
rotary  planer — The  profiling  machine — The  cam-cutting  machine — 
The  screw-thread  milling  machine— The  milling  cutter  grinder. 

THE  LINCOLN  MILLING  MACHINE 

As  already  mentioned,  the  milling  machine  was  invented  by 
Eli  Whitney.  It  appeared  in  a  variety  of  forms  during  the 
succeeding  years  but  "  the  beginning  of  practice  it  has  endured" 
is  found  in  the  Lincoln  milling  machine  designed  by  F.  A.  Pratt, 
when  a  foreman  at  the  Phoenix  Iron  Works  of  Hartford, 
Conn.,  during  the  early  fifties  of  the  last  century.  These 
works  were  then  owned  by  G.  S.  Lincoln  and  Company,  from 
whom  the  machine  takes  its  name. 

This  machine  is  one  of  the  most  striking  early  examples  of 
advanced  design,  as  no  machine  tool  has  suffered  so  little  change 
during  the  succeeding  years.  This  is  shown  by  Figs.  211  and 
2 1 2  of  which  the  former  is  reproduced  from  an  old  advertising 
circular  and  represents  one  of  Mr.  Whitney's  earliest  machines 
while  the  latter,  from  the  Pratt  and  Whitney  Company,  shows 
the  machine  as  made  to-day.  Except  that  the  latter  is  heavier 
and  provided  with  an  oil  pan,  it  is  scarcely  changed  from  the 
original.  No  form  of  milling  machine  has  been  made  in  such 
large  numbers.  It  is  suited  to  plain  work  only  and  it  lacks 
the  facility  of  adjustment  of  other  types  but  for  work  produced 
in  large  lots,  in  which  the  adjustment,  once  made,  is  retained 
for  a  long  period,  it  is  excellently  adapted,  while  its  simplicity 
and  low  cost  give  it  a  large  field  of  application. 

The  most  recent  development  in  connection  with  this  general 
type  of  machine  is  found  in  the  semi-automatic  machine  of 

224 


MILLING 


225 


226 


METHODS  OF  MACHINE  SHOP  WORK 


the  Cincinnati  Milling  Machine  Company,  Fig.  213.  The 
machine  shown  has  two  milling  heads  for  simultaneous  opera- 
tions on  both  sides  of  the  work,  although  single-head  machines 
are  also  made.  The  distinguishing  characteristic  of  the 
machine  is  the  provision  of  an  automatic  quick  return  to  the 
work  table  and  also  an  automatic  increase  in  the  forward  move- 
ment for  the  numerous  cases  in  which  the  surface  to  be  machined 
is  not  continuous. 

A  double  set  of  dogs  for  controlling  the  feed  mechanism  is 


FIG.  213. — Semi-automatic  plain  milling  machine. 

attached  to  the  side  of  the  work  table  as  shown.  The  work 
being  properly  chucked  and  one  of  the  hand  levers  tripped, 
the  table  goes  quickly  forward  at  a  rate  of  one  hundred  inches 
per  minute  until  the  first  surface  to  be  machined  reaches  the 
cutter,  when  the  motion  automatically  slows  down  to  what- 
ever feed  has  been  selected,  and  this  continues  until  one  of 
the  faces  is  milled.  As  soon  as  the  cutter  has  passed  this  first 
face,  the  table  automatically  speeds  up  again  to  one  hundred 


MILLING  227 

inches  per  minute,  until  the  second  face  of  the  work  reaches  the 
cutter.  Again  the  work  proceeds  at  the  feed  selected,  and  pass- 
ing the  second  face,  speeds  up  again,  then  slows  down  again 
when  the  third  face  is  reached,  feeds  along  the  third  face,  and 
when  this  is  completed,  the  table  automatically  returns  at  a 
rate  of  one  hundred  inches  per  minute  to  the  starting  point. 

As  many  dogs  as  may  be  necessary  for  the  work  may  be  placed 
on  the  table.  All  the  dogs  in  the  upper  slot  serve  to  slow  down 
from  the  quick  forward  motion,  bringing  the  table  movement 
to  the  proper  feed  rate.  The  left-hand  dog  in  the  lower  T-slot 
serves  to  trip  for  the  table  return,  and  the  right-hand  dog  in 
the  lower  T-slot  to  trip  for  the  stopping  of  the  table,  while  the 
other  dogs  in  the  lower  T-slot  are  so  arranged  as  to  speed  the 
table  up  from  the  feed  rate  to  the  quick  traverse  rate. 

Because  of  these  movements  these  machines  are  semi- 
automatic, that  is,  the  movements  of  the  table  are  entirely 
automatic,  but  the  chucking  of  the  work  and  the  starting  and 
stopping  of  the  machine  are  normally  controlled  by  the 
operator. 

As  these  pages  are  in  process  of  preparation  for  publication 
information  arrives  regarding  a  remarkable  increase  of  output 
by  the  Cincinnati  Milling  Machine  Company.  By  increasing 
the  quantity  of  cooling  liquid  far  beyond  what  is  customary, 
it  has  been  found  possible  to  increase  cutter  speeds  and  feeds 
to  from  eight  to  twelve  times  the  prevailing  figures.  Test 
cuts  in  mild  machinery  steel  have  been  made  at  peripheral 
cutting  speeds  of  800  feet  and  under  feeds  of  112  inches  per 
minute. 

THE  UNIVERSAL  MILLING  MACHINE 

The  first  radical  departure  from  the  Lincoln  machine  was  the 
invention  of  the  Universal  milling  machine  by  J.  R.  Brown  (he 
of  Brown  and  Sharpe)  in  1862.  The  object  of  the  swiveled 
table  and  the  spiral  feeding  mechanism  which  gives  the  machine 
its  universal  feature,  was  originally  the  making  of  twist  drills 
which  supplied  the  impelling  motive  of  the  design.  The 
first  universal  milling  machine  has  been  recovered  and  is 
preserved  by  the  Brown  and  Sharpe  Manufacturing  Com- 


228 


METHODS  OF  MACHINE  SHOP  \\ORK 


II 


r* 


I  ^'rm 


Hf..'W 


1    I 


MILLING 


229 


230  METHODS  OF  MACHINE  SHOP  WORK 

party,  and  of  it  Fig.  214  is  an  illustration  from  a  photograph, 
while  Fig.  215  is  a  small  modern  machine  by  the  same  makers 
and  serves  to  show  the  long  look  into  the  future  taken  by  Mr. 
Brown  in  the  original  design.  The  new  machine  has  a  constant- 
speed  pulley  in  place  of  the  cone-pulley  drive  and  a  geared  in- 
stead of  a  belt  feed.  Nevertheless,  in  the  essentials,  which 
make  it  a  universal  milling  machine,  it  is  scarcely  changed  and 
this  is  equally  true  of  similar  machines  by  other  makers. 

The  cone-pulley  drive  has  not  disappeared  from  the  milling 
machine,  but  for  heavy  manufacturing  the  constant-speed  pul- 
ley has  largely  displaced  it.  A  second  Brown  and  Sharpe 
machine  of  much  larger  size  is  shown  in  Fig.  216. 

In  this,  as  with  other  constant-speed  drive  machines,  the  dif- 
ferent speeds  are  obtained  by  a  nest  of  gears  within  the  machine 
which  are  thrown  into  various  combinations  by  the  projecting 
hand  levers. 

THE  CONSTANT-SPEED  PULLEY  DRIVE  AS  APPLIED  TO  MILLING 

MACHINES 

In  its  application  to  the  milling  machine  the  constant-speed 
pulley  drive  has  an  advantage  that  does  not  appear  in  other 
applications.  The  fact  that  the  first  motion  shaft  runs  at  a 
constant  speed  makes  it  possible  to  lay  out  a  series  of  feeds 
having  definite  values  in  inches  per  minute  and  to  mark  such 
values  on  the  index  plate  which  gives  the  positions  of  the  hand 
levers  which  control  the  acting  combinations  of  the  feed  gears. 
With  the  cone-pulley  drive  this  is  impossible,  since  the  rates  of 
feed  change  with  each  change  in  the  speed  of  the  first  motion 
shaft  as  determined  by  the  position  of  the  cone-pulley  belt. 
With  the  cone  pulley  drive,  the  rates  of  feed  can  only  be  given 
in  thousandths  of  an  inch  per  revolution  of  the  spindle — a  far 
less  convenient  arrangement  than  the  former  one. 

Increased  convenience  is,  however,  but  a  small  part  of  the 
advantage.  With  the  thousandths  per  revolution  feed,  a  rate 
of  feed  suitable  for  a  large  cutter  at  a  suitable  low  speed  is 
increased  in  proportion  to  the  cutter  speed  when  a  small 
cutter  is  substituted  for  the  large  one,  this  increase  being  so 
great  that  the  feed  becomes  useless  for  small  cutters.  Again, 


MILLING 


231 


a  rate  suitable  for  a  small  cutter  is  reduced  in  proportion  to  the 
cutter  speed  when  a  large  cutter  is  substituted  for  the  small 
one,  this  reduction  being  so  great  that  this  feed,  in  turn,  be- 
comes useless  for  large  cutters.  Whatever  the  size  of  the  cutter, 
only  a  small  part  of  the  entire  feed  range  is  applicable  to  it. 
With  the  inches  per  minute  feed,  on  the  contrary,  the  entire 
range  is  applicable  to  large  cutters  and,  except  for  their  in- 
adequate strength  for  heavy  cuts,  to  the  small  ones  also.  In 
order  to  provide  the  same  number  of  feeds  which  are  available 


FIG.  218. — Multiple  spindle  planer  type  milling  machine. 

for  cutters  of  different  sizes  a  much  greater  total  number  of 
feeds  must  therefore  be  provided  with  the  thousandths  per 
revolution  than  with  the  inches  per  minute  plan.  As  a  matter 
of  fact,  so  great  a  number  is  never  provided,  the  result,  whatever 
the  size  of  the  cutter,  being  a  restricted  choice  of  feeds. 

The  case  is  essentially  different  from  that  of  a  lathe,  boring  or 
drilling  machine.  In  these  latter  the  number  of  cutting  tools 
or  points  does  not,  usually,  increase  with  the  diameter  of  the 


232  METHODS  OF  MACHINE  SHOP  WORK 

work  and  a  feed  in  fractions  of  an  inch  per  turn  expresses  the 
duty  imposed  on  the  cutting  points.  With  the  milling  cutter, 
on  the  other  hand,  the  number  of  teeth  increases  with  the 
diameter  and  a  feed  per  turn  tells  nothing  about  the  duty  on 
the  teeth  until  divided  by  their  number,  nor  about  the  rate  at 
which  the  work  is  being  done  until  multiplied  by  the  revolutions 
of  the  cutter  per  minute.  A  feed  expressed  in  inches  per  minute, 
on  the  other  hand,  expresses  reasonably  well  the  duty  on  the 
teeth  and,  at  the  same  time,  the  exact  rate  at  which  the  work  is 
being  done. 

For  certain  classes  of  milling-machine  work  the  vertical 
spindle  has  advantages  over  the  horizontal  and  a  rugged  vertical- 
spindle  machine  by  the  Cincinnati  Milling  Machine  Company 
is  shown  in  Fig.  217.  Machines  of  the  planer  type  have  also 
reached  large  development,  such  a  machine  by  the  Ingersoll 
Milling  Machine  Company  being  shown  in  Fig.  218. 

CUTTERS  OF  MILLING  MACHINES 

The  cutters  used  on  milling  machines  are  of  a  great  variety 
of  types,  of  which  a  few  are  shown  in  Figs.  219-230.  Of  these 
the  most  common  is  the  slabbing  cutter,  Fig.  219,  the  illustration 
showing  a  cutter  with  nicked  teeth,  which  construction  is  ad- 
vantageous by  reason  of  its  action  in  breaking  up  the  chips. 
Fig.  2  20  shows  a  side  or  face  cutter  with  which  the  chief  cutting 
action  is  on  the  side  and  Fig.  221  a  pair  of  interlocking  side 
cutters  intended  for  cutting  grooves  or  slots.  The  object  of  the 
construction  is  to  preserve  the  width  of  the  slot  after  the  cutter 
is  ground,  in  which  case  the  cutters  are  packed  apart  by  paper 
washers  placed  between  them — the  interlocking  teeth  still 
giving  a  satisfactory  cutting  action.  Fig.  222  shows  a  face 
cutter  with  inserted  teeth.  There  are  many  methods  of  secur- 
ing teeth  in  position  of  which  but  one  is  shown.  The  object  of 
the  construction  is  to  save  cost  by  the  use  of  cheaper  material 
on  the  body  of  large  cutters.  With  such  a  construction  new 
teeth  may  be  inserted  when  the  old  ones  are  worn  out  and  the 
use  of  the  body  be  continued  indefinitely.  Fig.  223  shows  an 
end  mill  and  Fig.  224  a  T  slot  cutter,  the  two  being  used  in 
succession  and  in  the  order  named  for  the  production  of  the 


MILLING 


233 


234  METHODS  OF  MACHINE  SHOP  WORK 

numerous  T  slots  which  appear  in  machine  tools  of  which  a 
section  is  shown  in  Fig.  225.  Fig.  226  is  an  angle  cutter. 
Fig.  227  is  a  shape  cutter  and  Figs.  228-230  are  formed 
cutters,  these  two  types  being  quite  distinct.  The  shape  cutter, 
like  all  the  others  previously  shown,  is  sharpened  when  dull  by 
grinding  the  edges  of  the  teeth — a  process  which  is  obviously 
applicable  to  simple  forms  only.  The  formed  cutter l  on  the 
other  hand  is  ground  on  the  faces  of  the  teeth  radial  with  the 
cutter.  The  cutter  being  made  of  proper  outline  this  outline  is 
not  changed  in  the  act  of  grinding  which  may  be  repeate-d  until 
the  cutter  is  worn  out.  These  formed  cutters  are  frequently 
made  for  the  production  of  pieces  of  complex  outline  as  shown  in 
Fig.  229,  for  which  purpose  they  are  very  suitable.  Their 
largest  use  and  the  use  for  which,  judging  by  the  illustration  of 
the  patent,  they  were  originally  invented  by  Mr.  Brown,  was  the 
production  of  cut  gears,  a  cutter  for  this  purpose  being  shown  in 
Fig.  230. 

TYPICAL  MILLING-MACHINE  OPERATIONS 

The  operations  of  which  the  milling  machine  is  capable  are 
so  numerous  as  to  almost  defy  enumeration.  A  few  of  them 
are  shown  in  Figs.  231-239,  from  the  Cincinnati  Milling 
Machine  Company.  Simple  surfacing  by  cylindrical  or  slab- 
bing cutters  is  too  common  an  operation  to  need  illustrating. 
Surfacing  by  a  face  cutter  on  a  vertical-spindle  machine  is 
shown  in  Fig.  23 1,  while  Fig.  23  2  shows  a  development  by  which 
the  work  of  the  cutter  is  made  continuous.  A  supplementary 
rotary  work  table  is  mounted  on  the  regular  table  and  carries 
a  number  of  special  chucks  for  holding  the  work — in  this  case 
domestic  sad  irons.  The  operator  removes  the  finished  pieces 
and  substitutes  rough  castings  for  them  without  stopping 
the  movement  of  the  rotary  table.  A  case  of  gang  milling 
with  a  combination  of  slabbing  and  face  mills  is  shown  in  Fig. 
233,  while  Fig.  234  shows  the  production  of  a  curved  outline 
by  a  formed  cutter.  A  costly  outfit  for  the  wholesale  produc- 
tion of  racks  is  shown  in  Fig.  235 — costly  not  only  because  of  the 
number  of  cutters  involved  but  also  because  the  pitch  of 

1  The  formed  cutter  was  invented  by  J.  R.  Brown. 


MILLING 


235 


FIG.  231. — Face  milling  on  a  vertical  spindle  machine. 


FIG.  232. — Continuous  face  milling. 


236 


METHODS  OF  MACHINE  SHOP  WORK 


FIG.  233. — Gang  milling. 


FIG.  234. — Formed  cutter  milling. 


MILLING 


FIG.  235. — Rack  cutting  by  a  gang  of  cutters. 


FIG.  236. — Rack  cutting  by  a  single  cutter. 


238 


METHODS  OF  MACHINE  SHOP  WORK 


FIG.  237. — Cutting  bevel  gears. 


FIG.  238. — Drilling  an  index  plate. 


MILLING  239 

the  rack  teeth  is  determined  by  the  spacing  of  the  cutters,  which 
must  be  of  high  accuracy.  A  more  common  method  of  cut- 
ting racks  is  shown  in  Fig.  236,  in  which,  by  a  right-angle 
fixture,  the  cutter  spindle  is  located  in  line  with  the  longitudinal 
movement  of  the  work  table.  The  spacing  of  the  teeth  is 
effected  by  suitably  indexing  the  movement  of  the  table.  Fig. 
23  7  shows  the  dividing  head  as  set  up  for  cutting  bevel  gears, 
the  spacing  of  the  teeth  being  by  the  index  plate,  while  another 
use  of  the  dividing  head  and  index  plate  for  the  production  of 
a  drilled  index  plate  is  shown  in  Fig.  238.  Finally,  the 
universal  function  of  the  machine  in  the  production  of  a 
helical-toothed  slabbing  cutter  is  shown  in  Fig.  239.  The  work 
table  is  swiveled  to  the  angle  of  the  cutter  while,  by  the 
change  gears  shown,  the  work  revolves  as  the  work  is  fed  for- 
ward. The  spacing  of  the  teeth  is  by  the  index  plate. 

THE  ROTARY  PLANER 

The  inserted  tooth  face  mill  frequently  assumes  large  diam- 
eters and  is  used  for  producing  large  flat  surfaces  by  means  of 
machines  which,  although  true  milling  machines,  are  com- 
monly called  rotary  planers.  A  striking  development  of  this 
machine  is  seen  in  Fig.  240  from  the  works  of  the  Allis  Chal- 
mers Company.  The  machines,  of  which  there  are  two,  by  the 
Niles-Bement-Pond  Company,  are  identical  except  that  they 
are  of  opposite  hand.  They  are  mounted  upon  a  cast-iron 
floor  plate  with  adjusting  screws  connecting  them  at  each  end, 
one  of  which,  with  the  threads  covered,  appears  in  the  immediate 
foreground.  The  object  of  these  screws  is  to  adjust  the  distance 
between  the  machines  and  maintain  them  parallel.  The  cut- 
ter heads  are  of  ten  feet  diameter  and  are  driven  by  motors  of 
forty  horse  power,  giving  a  capacity  for  cuts  in  cast  iron  one  and 
one-quarter  inches  deep  with  one  and  one-half  inches  per  min- 
ute feed  for  roughing  cuts.  For  finishing  cuts  feeds  as  high 
as  four  inches  per  minute  are  used.  The  work  in  progress  is 
the  simultaneous  surfacing  of  the  top  and  bottom  faces  of  a 
large  Corliss  engine  cylinder. 

Another  application  of  rotary  planers,  in  this  case  by  the 
Newton  Machine  Tool  Works,  and  from  the  same  works  as 


240 


METHODS  OF  MACHINE  SHOP  WORK 


FIG.  239. — Helical  milling. 


FIG.  240. — Twin  rotary  planers. 


MILLING 


241 


FIGS.  241  and  242.— Machining  fly  wheel  segments. 


16 


242  METHODS  OF  MACHINE  SHOP  WORK 

the  last  one,  is  shown  in  Figs.  241  and  242.  The  work  here 
in  progress  is  the  machining  of  the  segments  of  large  fly  wheels, 
the  operations  being  of  a  character  which  fairly  entitles  them  to 
be  called  manufacturing  methods.  Two  rotary  planers  are 
employed  which,  as  before,  are  mounted  on  a  cast-iron  floor 
plate.  In  Fig.  241  the  two  machines  are  so  located  as  to 
machine  the  ends  of  the  segments  to  the  angle  required.  Various 
angles  are  scribed  upon  the  floor  plate  by  means  of  which  the 
adjustable  machine  may  be  quickly  located  for  wheels  with  any 
number  of  segments.  With  the  radial  joints  complete,  the 
machines  are  adjusted  parallel  with  one  another  and  at  suit- 
able distances  apart  to  machine  the  two  sides  of  the  hub  ends 
of  the  segments  as  shown  in  Fig.  242. 

THE  PROFILING  MACHINE 

A  modification  of  the  milling  machine  which  was  developed 
at  Hartford  and  Springfield  during  the  Civil  War  period  is  the 
profiling  machine  which  is  best  introduced  by  showing  the  work 
to  which  it  is  adapted.  This  work  is  still  chiefly  the  parts  of 
small  arms  as  shown  in  Fig.  243,  the  curved  outlines  of  the 
pieces  shown  being  made  by  the  profiling  machine.  The  work 
done  will  be  seen  to  be  that  which,  in  former  days,  was  done  with 
the  filing  jig  shown  in  Fig.  2. 

A  profiling  machine  by  the  Pratt  and  Whitney  Company  is 
shown  in  Fig.  244.  The  milling  head  is  fitted  to  slide  on  the 
overhead  cross  rail  on  which  its  movements  are  controlled  by 
the  hand  crank  at  the  right  through  the  gearing  shown.  A 
second  hand  crank  at  the  left  gives  movement  to  the  work  table 
at  right  angles  to  the  movement  of  the  cutter  spindle.  In 
use,  the  blank  piece  of  work  is  secured  to  the  work  table  and 
alongside  of  it  a  model  or  former,  shaped  to  the  exact  outline 
of  the  desired  piece.  At  each  side  of  the  cutter  spindle,  at  its 
lower  end,  is  a  clamp  socket.  In  one  or  the  other  of  these, 
according  to  convenience,  a  pin  of  the  exact  diameter  of  the 
milling  cutter  is  inserted.  When  at  work  the  operator,  by 
suitable  manipulation  of  the  cranks,  brings  the  pin  into  contact 
with  the  former  and  then  traverses  it  around  the  former,  follow- 


MILLING 


243 


bfl 

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-s 

oi 

a 
.s 

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I 


244  METHODS  OF  MACHINE  SHOP  WORK 

ing  its  profile  exactly,  the  result  being  to  reproduce  the  same 
profile  in   the  piece  of  work 

THE  CAM-CUTTING  MACHINE 

Another  important  modification  of  the  milling  machine  is 
found  in  the  cam-cutting  machine  of  which  an  example,  by  the 
Garvin  Machine  Company,  is  shown  in  Figs.  245  and  246. 
Cams  are  of  two  chief  varieties,  called  respectively  face  and 
drum  cams.  The  face  cam  is  a  disc  with  an  irregular  shaped 
groove  in  its  face  for  the  production  of  a  movement  radial  to 
itself.  The  drum  cam,  on  the  other  hand,  is  a  cylinder  with  a 
groove  in  its  periphery  for  producing  a  movement  parallel 
with  its  center  line.  The  machine  is  shown  as  set  up  for  the 
production  of  both  kinds  of  cams.  As  in  the  profiling  machine, 
the  milling  cutter  which  produces  the  groove  in  the  cam  is 
guided  by  a  former  having  the  exact  outlined  desired  but,  unlike 
the  profiling  machine,  the  feed  is  by  power  and  not  by  hand. 

Referring  to  Fig.  245,  which  shows  the  machine  in  the  act 
of  producing  a  face  cam,  two  worm-driven  turntables  will  be 
seen  mounted  on  the  work  table.  The  turntables  revolve 
slowly  and  in  unison,  the  one  in  the  background  carrying  the 
hand-made  former1  while  the  one  in  the  foreground  carries  the 
cam  blank  in  process  of  being  cut.  A  long  ribbed  head  slides 
upon  the  cross  rail  and  carries,  depending  from  it,  a  pin  at  its 
farther  and  a  milling  cutter  at  its  nearer  end — the  pin  and 
cutter  being  of  the  same  diameter.  The  pin  is  held  in  contact 
with  the  former  by  a  weight  suspended  from  a  chain  which,  pass- 
ing over  a  sheave,  is  attached  to  the  sliding  head.  As  the  cam 
and  former  revolve  under  the  action  of  the  feed,  the  action 
of  the  former  is  to  reciprocate  the  sliding  head  in  accordance 
with  its  own  profile,  and  this  movement  being  transmitted  to 
Uie  milling  cutter,  the  latter  reproduces  in  the  cam  blank  the 
outline  of  the  former. 

Fig.  246  shows  the  machine  as  arranged  for  the  production 
of  drum  cams.  The  cam-holding  turntable  of  the  previous 
frustration  has  been  removed  and  in  its  place  is  a  suitable  drum- 

1  The  methods  by  which  cams  are  laid  out,  including  the  making  of  the  formers, 
may  be  found  in  the  author's  Handbook  for  Machine  Designers  and  Draftsmen. 


MILLING 


245 


246 


METHODS  OF  MACHINE  SHOP  WORK 


cam  fixture.  As  before,  the  former  is  at  the  left  and  the  cam 
blank  at  the  right.  The  two  being  mounted  on  the  same 
arbor,  the  action  as  this  arbor  revolves  is  to  reproduce  the  out- 
line of  the  former  in  the  cam  blank  essentially  as  in  the  previous 
illustration. 

THE  SCREW-THREAD  MILLING  MACHINE 

Another  modification  of  the  milling  machine  is  found  in  the 
thread  or  screw  milling  machine,  originally  developed  by  the 
Pratt  and  Whitney  Company,  one  of  whose  machines  is  shown 
in  Fig.  247.  This  machine  may  be  regarded  as  a  combination 
of  the  lathe  and  the  milling  machine.  Combined  with  the 
general  form  of  a  lathe,  with  the  construction  of  a  lathe 


FIG.  247. — Screw  thread  milling  machine. 

so  far  as  the  means  for  determining  the  pitch  of  the  screw  are 
concerned,  is  a  milling  machine  head  carrying  a  milling  cutter 
in  place  of  the  usual  lathe  tool.  The  cutter  head  is  provided 
with  the  necessary  adjustment  for  adapting  the  angle  at  which 
the  cutter  lies  to  the  helix  angle  of  the  thread  to  be  cut. 

Still  another  modification  is  the  hobbing  machine  of  which 
an  example,  by  the  Newton  Machine  Tool  Works,  has  already 
been  shown  in  Fig.  43. 

Both  hobbing  and  cam  cutting  are  frequently  done  by  extern- 


MILLING  247 

porized  apparatus,  the  former  frequently  mounted  on  a  lathe 
and  the  latter  on  a  milling  machine,  but  no  examples  of  such 
equipments  are  here  shown. 

THE  MILLING  CUTTER  GRINDER 

An  essential  adjunct  of  the  milling  machine  is  the  cutter 
grinder  of  which  one,  by  the  Brown  and  Sharpe  Manufacturing 
Company,  is  shown  in  Fig.  248.  This  particular  machine  is 
also  adapted  to  the  doing  of  small  tool-room  work  of  the  char- 
acter done  on  the  universal  grinding  machine,  but  the  features 
which  here  engage  us  are  those  by  which  milling  cutters  and 
similar  tools  are  sharpened.  To  accommodate  the  various  types 
of  cutters,  extreme  flexibility  of  adjustment  in  a  cutter  grinder 
is  essential.  Without  the  exception  of  even  the  universal  milling 
machine,  the  center  grinder  is  capable  of  doing  a  greater  variety 
of  work  than  any  other  machine  tool  and  of  these  it  is  only 
possible  to  show  a  few  of  the  more  representative  examples. 

Fig.  248  gives  a  comprehensive  view  of  the  working  parts  of 
the  machine  and  also  shows  it  adjusted  for  sharpening  an  angle 
cutter,  the  angle  being  obtained  by  the  swivel  of  the  work  table. 
The  angle  is  read  from  the  divided  arc  on  the  front  of  the  table. 
Fig.  249  shows  the  grinding  of  the  most  common  of  all  milling 
cutters — the  slabbing  cutter.  A  cupped  grinding  wheel  is 
used,  thereby  grinding  flat  faces  to  the  teeth  instead  of  concave 
faces  which  would  be  the  result  of  grinding  with  a  common  disc 
wheel.  A  feature  of  the  machine  which  is  less  clearly  shown  in 
some  of  the  views  than  others,  but  which  is  always  present,  is 
the  spring  tooth  rest  shown  clearly  in  Fig.  249,  which  projects 
up  from  below  and  against  which  the  tooth  being  ground  rests. 
The  cutter  is  slid  endwise  on  its  supporting  arbor  by  the  hand, 
contact  with  the  rest  being  maintained  by  gentle  pressure  and, 
as  each  tooth  is  finished,  the  cutter  is  turned  to  present  the 
next  one  to  the  wheel,  the  spring  of  the  rest  enabling  it  to  give 
way  and  snap  past  the  teeth. 

Figs.  250  and  251  show  the  adjustments  for  grinding  a  face 
cutter,  in  one  case  that  for  the  periphery  and  in  the  other 
for  the  side,  the  latter  showing  also  an  adjustment  of  the  tool- 
carrying  head  which  is  frequently  required  for  other  pieces  of 


248 


METHODS  OF  MACHINE  SHOP  WORK 


MILLING  249 

work.  The  tooth  rest  is  also  clearly  shown  in  this  view.  Fig. 
252  shows  the  grinding  of  a  convex  shape  cutter  to  a  circular 
profile  by  means  of  a  swivel  attachment  provided  for  that  pur- 
pose, and  Fig.  253  shows  the  adjustment  for  grinding  large 
inserted  tooth  cutters. 


CHAPTER  XII 
GEAR  CUTTING 

Multiplicity  of  forms  of  gear-cutting  machines — The  advantages  of  the 
diametrical  pitch  system — The  three  basic  systems  of  gear  cutting — 
Machines  embodying  these  systems— Bevel  gear-cutting  machines — 
The  octoid  system  of  bevel  gear  teeth — Gear-molding  machines. 

VARIETY  OF  GEAR-CUTTING  MACHINES 

There  is  no  feature  of  machine  work  of  greater  interest  than 
gear  cutting,  as  there  is  none  to  which  so  great  a  degree  of 
attention  has  been  directed  and  with  correspondingy  fruitful 
results.  There  is  no  other  example  of  a  single  purpose  machine 
that  has  been  produced  in  such  a  bewilderng  diversity  of 
forms.  It  is  impossible  to  give  here  more  than  an  outline  of  the 
leading  methods  of  attacking  the  gear-cutting  problem  with 
sufficient  illustrations  to  show  how  these  methods  are  embodied 
in  commercial  machines.  For  additional  information  the 
reader  is  referred  to  the  excellent  treatise,  Gear  Cutting  Machin- 
ery, by  Ralph  E.  Flanders,  wherein  will  be  found,  with  but 
one  or  two  exceptions,  all  the  machines  now  made,  both  American 
and  European.1 

ADVANTAGES  OF  THE  DIAMETRAL  PITCH  SYSTEM  OF  GEARS 

The  diametral  pitch  system  is  at  the  base  of  all  modern 
cut  gears  of  moderate  size.  This  system,  as  already  stated,  was 
invented  by  Bodmer  but  introduced  as  a  general  commercial 
system  by  the  Brown  and  Sharpe  Manufacturing  Company. 
Coincident,  or  nearly  coincident  with  this  introduction,  the 
Brown  and  Sharpe  Company  developed  and  published  in  their 
catalogue  a  set  of  simple  formulas  for  the  calculation  of  gears, 
singly  and  in  pairs.  These  formulas,  which  have  been  copied 

1  Figs.  254,  257,  259  and  267  are,  by  permission,  reproduced  from  Mr.  Flander's 
treatise. 

250 


GEAR  CUTTING  251 

into  all  American  mechanical  engineer's  pocket  books,  have 
influenced  beyond  measure  the  introduction  of  the  diametral 
pitch  system. 

The  superior  convenience  of  the  diametral  pitch  system  is 
largely  due  to  the  simplicity  of  these  formulas  and  of  the  resulting 
calculations.  A  series  of  standard  pitches  is  selected,  analogous 
to  the  series  of  pitches  of  standard  screw  threads,  an  indefinite 
number  of  intermediate  pitches  which  might  be  used  being  dis- 
carded, thus  making  systematized  cutter  manufacture  possible. 
By  thus  giving  up  complete  liberty  of  choice  in  the  matter  of 
the  pitch,  corresponding  liberty  of  choice  of  diameters  is  sacri- 
ficed. So  far  as  the  pitches  themselves  are  concerned,  this  gives 
rise  to  just  as  little  inconvenience  in  the  case  of  the  gears  as  in 
that  of  screw  threads.  It  does,  however,  lead  to  an  occasional 
slight  inconvenience  in  connection  with  the  diameters  and  center 
distances.  Since  a  gear  must  contain  a  whole  number  of  teeth, 
it  follows  that,  for  any  given  pitch,  only  such  diameters  are 
possible  as  will  contain  an  exact  whole  number  of  teeth,  the 
diameters  for  any  one  pitch  varying  by  a  series  of  steps  precisely 
as  the  pitches  vary.  This  series  of  diameters  differs,  of  course, 
with  the  pitch. 

Thus  considering  eight  pitch — that  is  a  pitch  such  that  the 
gear  contains  eight  teeth  for  each  inch  of  its  pitch  diameter — a 
gear  of  sixteen  teeth  will  be  of  two  inches  pitch  diameter.  Simi- 
larly, a  gear  of  seventeen  teeth  will  be  of  two  and  one-eighth  and 
one  of  eighteen  teeth  of  two  and  one-quarter  inches  pitch  diam- 
eter, no  diameter  between  these  values  being  possible  if  gears 
of  eight  pitch  are  to  be  used.  This  feature  requires  attention 
in  the  design  by  giving  the  gear  centers  such  locations  as  will 
provide  for  the  necessary  diameters. 

Another  essential  and  valuable  feature  of  the  diametral  pitch 
system  is  that  the  diameters  of  the  gears  and  the  distances  be- 
tween centers  are  always  expressed  in  even  fractions  and  are 
never  incommensurate.  In  the  circumferential  pitch  system, 
since  the  pitch  is  commensurate,  the  circumference  is  also 
commensurate,  while  the  diameters  and  center  distances  are  in- 
commensurate. With  the  diametral  pitch  system  the  reverse 
is  true.  The  circumferential  pitch  of  gears  made  on  this  system 


252 


METHODS  OF  MACHINE  SHOP  WORK 


is  incommensurate  as  is  the  circumference,  but  the  diameters 
and  center  distances  are  always  commensurate  and,  while  com- 
mensurate circumferences  have  no  particular  value,  commen- 
surate diameters  and  center  distances  are  sources  of  many 
conveniences. 

THE  SYSTEMS  OF  GEAR  CUTTING 

There  are  three  basic  systems  of  gear  cutting:  (a)  the  formed 
tool  system;  (b)  the  generating  system,  of  which  the  hobbing 
system  is  a  development  and,  (c)  the  templet  system. 


FIG.  254. — Principle  of  the  formed  tool  system  of  gear  cutting. 

Of  these  the  oldest  and  most  widely  used  is  the  formed-tool 
system,  of  which  the  principle  is  illustrated  in  Fig.  254.  The  tool, 
which  might  be,  and  sometimes  is,  a  planing  tool  as  shown  at 
the  top  of  the  illustration  but  which,  in  the  vast  majority  of 
cases,  is  a  rotary  milling  cutter  as  shown  at  the  bottom  of  the 
illustration,  is  accurately  formed  to  the  desired  profile  which  it 
reproduces  in  the  gear.  It  was  for  this  purpose  that  the 
formed  cutter  which  may  be  sharpened  by  grinding  without 
changing  its  form  was  originally  invented. 

Machines  embodying  this  principle  were  first  made  in  England. 


GEAR  CUTTING 


253 


"8 


254  METHODS  OF  MACHINE  SHOP  WORK 

The  first  to  perform  their  functions  automatically,  requiring  no 
attention  on  the  part  of  the  operator  except  to  remove  a  com- 
pleted gear  and  supply  its  place  with  a  fresh  blank  were  made  by 
William  Sellers  and  Company  in  1866,  some  of  the  machines  then 
made  being  still  in  use  at  the  Sellers  works.  The  Sellers  machine 
was  ahead  of  its  time  and,  while  some  were  sold,  they  were  not 
placed  on  the  general  market,  the  first  commercial  automatic 
machine  being  produced  by  the  Brown  and  Sharpe  Manufactur- 
ing Company  in  1877.  This  machine,  which  has  supplied  the 
model  for  many  others,  is  shown,  as  now  made,  in  Fig.  255, 
and  were  the  original  machine  placed  beside  it  even  fewer 
changes  would  be  found  than  in  the  universal  milling  machine. 
It  is  not  the  author's  purpose  to  go  into  detailed  description  of 
the  operation  of  this  or  other  complex  machines,  the  intention 
being  to  point  out  the  principles  of  the  work  and  the  general 
methods  by  which  the  various  problems  are  attacked. 

The  action  is  entirely  automatic,  the  feed  and  return  of  the 
cutter  and  the  indexing  of  the  blank  from  tooth  to  tooth  requir- 
ing no  attention  on  the  part  of  the  operator  who  has  but  to 
remove  the  completed  gears  and  supply  their  place  with  fresh 
blanks.  For  larger  work  convenience  of  handling  leads  to  the 
horizontal  instead  of  the  vertical  position  for  the  gear  in  process 
of  being  cut.  Automatic  machines  have  been  made  for 
cutting  gears  of  large  size  but,  usually,  such  machines  are  non- 
automatic,  an  example,  by  the  Newton  Machine  Tool  Works, 
being  shown  in  Fig.  256. 

For  the  largest  work,  gear-cutting  machines  operate  more 
frequently  on  the  templet  principle,  an  example  of  this  con- 
struction appearing  on  a  later  page. 

THE  GENERATING  SYSTEM  OF  GEAR  CUTTING 

The  generating  system  was  invented  by  Hugo  Bilgram  who 
produced  his  first  machine  in  1885.  This  machine  was  invented 
for  the  production  of  bevel  gears  for  which  at  that  time  no 
satisfactory  method  of  production  was  available. 1  The  system 

1  A  machine  for  the  production  of  correct  bevel  gears  was  exhibited  at  the 
Centennial  Exposition  of  1876  by  George  H.  Corliss.  The  machine  was  of  large 
size  suitable  for  the  production  of  mill  gearing.  It  was  constructed  especially 


GEAR  CUTTING 


255 


has  now  been  adapted  to  the  production  of  spur  and  spiral 
gears  and  the  principle  is  best  described  in  connection  with 
spur  gears.  At  the  top  in  Fig.  257  is  a  gear  of  metal  while 
below  it  is  a  blank  of  some  plastic  material.  If  the  two  shafts 
be  connected  by  gears  having  their  speed  ratio  equal  to  that 
between  the  pitch  diameters  of  the  forming  gear  and  the  plastic 
blank  and  the  two  be  revolved  together,  the  forming  gear  will 
impress  into  the  plastic  blank  tooth  forms  which  are  conjugate 


FIG.   257. — Principle  of  the  generating  system  of  gear  cutting. 

to  those  of  the  forming  gear  and  which,  if  in  metal,  would  form 
suitable  teeth  for  a  gear  to  mate  with  the  forming  gear. 

If  the  forming  gear  be  made  of  hardened  steel  with  suitable 
rake  and  clearance  to  the  teeth,  and  if  it  be  then  reciprocated 
on  its  center  line  as  the  rotation  proceeds,  the  plastic  blank 
may  be  replaced  by  a  metallic  blank,  the  teeth  of  the  forming 
gear  acting  as  cutting  tools  to  generate  correct  mating  gear 

to  cut  the  transmission  gears  of  the  monumental  Corliss  engine  which  supplied 
power  for  Machinery  Hall  of  the  Exposition  and,  among  engineers,  it  attracted 
almost  as  much  attention  as  the  engine.  It  operated  on  the  templet  principle 
which  was  subsequently  made  commercial  by  the  Gleason  works,  who  produced 
a  machine  that  came  into  large  use. 


256  METHODS  OF  MACHINE  SHOP  WORK 

teeth.     It  is  exactly  upon  this  principle  that  the  Fellows  gear 
shaper  operates. 

In  this  system  the  forming  gear  cutter  might  be  a  rack  which 
would  then  produce  in  blanks  of  various  sizes,  teeth  which  are 
conjugate  to  those  of  the  rack  and  to  each  other.  In  the 
involute  system  the  sides  of  rack  teeth  are  straight,  whereas 
the  sides  of  all  gear  teeth  are  curved.  A  straight-sided  tool  is 
an  easy  thing  to  originate  with  a  high  degree  of  accuracy  and 
hence,  in  all  applications  of  the  generating  system,  the  straight- 
sided  rack  tooth  forms  at  least  the  starting  point.  In  its  orig- 
inal appearance  on  the  Bilgram  bevel  gear  machine  the  straight- 
sided  rack  tooth  forms  the  cutting  tool.  This  is  not  to  be 
understood  as  meaning  that  an  actual  rack  is  used  in  the 
machine  but  a  cutting  tool  which  represents  a  single  tooth  of 
the  rack  or,  more  properly,  one  side  of  that  tooth  because,  the 
spaces  between  bevel  gear  teeth  being  tapered,  but  one  side 
can  be  formed  at  a  time. 

THE  BILGRAM  BEVEL  GEAR  GENERATING  MACHINE 

Mr.  Bilgram's  original  bevel  gear-cutting  machine,  as  it 
appeared  in  the  American  Machinest  for  May  9,  1885,  is  shown 
in  Fig.  258.  The  machines  now  made  are  fully  automatic  in 
their  action  which  the  machine  shown  was  not.  It  is  here  used 
in  preference  to  the  modern  machines,  partly  because  of  its 
historic  interest  and  partly  because  its  comparative  simplicity 
makes  its  principle  of  action  more  apparent. 

The  straight-sided  tool  which  represents  one  side  of  a  rack 
tooth — in  the  case  of  bevel  gears  more  properly  a  crown  gear 
tooth — is  mounted  upon  a  ram  driven  precisely  like  a  shaping 
machine  ram.  The  gear  blank  is  mounted  below  the  tool  upon  a 
suitable  arbor  supported  at  its  rear  end  by  a  conical  segment 
which  rolls  upon  a  plane  surface  below  it.  The  conical  seg- 
ment is  a  portion  of  the  pitch  surface  of  the  gear  to  be  cut, 
extended  to  the  opposite  nappe  of  the  cone,  while  the  plane 
surface  is  a  portion  of  the  pitch  surface  of  the  imaginary  crown 
gear  of  which  the  cutting  tool  represents  one  side  of  a  tooth. 
Integrity  of  the  rolling  motion  without  slip  is.  maintained  by  a 


GEAR  CUTTING 


257 


pair  of  steel  ribbons,  one  end  of  each  of  which  is  clamped  to 
the  end  of  the  rolling  segment  and  the  other  end  to  the  oppo- 
site end  of  the  stationary  plate. 

If  the  segment  be  rolled  upon  the  plate  the  gear  blank  will 
roll  past  the  cutting  tool  precisely  as  though  the  latter  were  a 
crown  gear  and,  with  the  tool  in  reciprocating  motion,  it  will 
cut  upon  the  gear  blank  a  suitably  formed  tooth  side  when,  the 
gear  blank  being  indexed  for  the  next  tooth  and  the  action 
repeated,  the  side  of  that  tooth  is  formed  and  so  on  indefinitely. 


FIG.  258. — The  original  Bilgram  bevel  gear  cutter,  generating  system. 

The  action  is,  perhaps,  more  clearly  shown  in  Fig.  259. 
Were  the  gear  being  cut  a  spur,  a  complete  rack  tooth  could 
be  used  as  at  a,  but  when  cutting  a  bevel  gear  the  taper  of  the 
space  between  the  teeth  makes  it  necessary  to  use  a  single-sided 
tool  as  at  b — a  second  tool  symmetrical  with  the  first  planing 
the  second  side  after  the  first  is  completed.  The  teeth  are 
roughed  out  in  a  preparatory  machine  before  the  generating 
machine  is  brought  into  action. 

17 


258 


METHODS  OF  MACHINE  SHOP  WORK 


THE   GLEASON  BEVEL  GEAR  GENERATING  MACHINE 

Consideration  of  Fig.  259  will  show  two  modifications  of  the 
plan  of  attack.  The  imaginary  rack  may  be  fixed  as  regards 
endwise  motion,  the  blank  rolling  past  it  as  a  gear  might  be 
rolled  in  a  rack,  this  being  the  plan  incorporated  in  the  Bilgram 
machine.  On  the  other  hand,  the  rack  may  travel  endwise 
with  the  feed,  the  gear  blank  turning  upon  its  center  which 
does  not  change  its  position.  This  latter  plan  of  attack  is 
incorporated  in  the  Gleason  machine  shown  in  Figs.  260 
and  261. 

The  gear  in  process  of  being  cut  appears  in  both  views 
mounted  on  the  horizontal  main  spindle.  Both  sides  of  the 

ideal  crown  gear  tooth  are  repre- 
sented by  tools  of  which  there  are 
two,  by  which  construction  both  sides 
of  a  tooth  are  shaped  simultaneously. 
These  tools  are  mounted  and  re- 
ciprocate in  guides  on  an  arm  which 
oscillates  about  the  cone  center  of  the 
gear  blank  being  cut,  this  oscillation 
being  obtained  by  the  horizontal  yoke 
and  vertical  connecting  rod  shown 
in  Fig.  261.  The  yoke  is  secured  to 
the  main  spindle  as  shown  in  Fig.  261 
and  carries  a  segment  gear  shown  in  the  same  view,  the  pitch 
cone  of  this  segment  being  identical  with  that  of  the  gear  blank 
being  cut.  Mounted  on  the  tool-carrying  arm  is  a  second  seg- 
ment gear  in  mesh  with  the  first,  also  shown  in  Fig.  261.  The 
second  segment  is  a  segment  of  a  crown  gear,  its  pitch  plane 
(pitch  cone  having  a  cone  angle  of  ninety  degrees)  being  identical 
with  that  of  the  ideal  crown  gear  tooth  represented  by  the 
cutting  tools.  As  the  yoke  oscillates  it  turns  the  gear  blank 
with  it  while  the  meshing  of  the  segments  compels  the  tool 
arm  to  oscillate  and  to  carry  the  cutting  tools  past  the  blank 
in  the  same  relation  as  a  crown  gear  tooth  in  mesh  with  a 
tooth  on  the  blank.  The  action  of  the  machine  is  fully 
automatic. 


Rack 


FIG.     259.—  Generating     gear 

teeth  from  a  rack  tooth. 


GEAR  CUTTING 


259 


FIG.  260. 


FIG.  261. 
Gleason  bevel  gear  cutting  machine,  generating  system. 


260 


METHODS  OF  MACHINE  SHOP  WORK 


THE  OCTOID  SYSTEM  OF  BEVEL  GEAR  TEETH 

When  inventing  his  machine,  Mr.  Bilgram  also  invented, 
incidentally,  an  entirely  new  tooth  form  system  which  is  neither 
involute  nor  epicycloidal.  This  system  appears  in  all  generated 
bevel  gears,  there  being  no  spur  gear  tooth  form  analogous  to  it. 

The  starting  point  of  the  system  is  the  straight-sided  crown 
gear  tooth  which  determines  the  outlines  of  all  gears  cut  by  it. 
It  so  happens  that  while  the  crown  gear  among  bevel  gears  is 
analogous  to  the  rack  among  spur  gears  its  teeth  do  not  have  a 
straight  side  as  do  rack  teeth. 

The  involute  rack  tooth  has  a  straight  side  because,  as  alimit- 


FIG.  262. — The  octold  crown  gear 
tooth. 


FIG.  263. — The  spherical  involute 
crown  gear  tooth. 


ing  construction,  its  center  of  curvature  goes  off  to  infinity.  In  a 
crown  gear,  however,  the  center  of  curvature  does  not  go  off  to 
infinity,  the  curve  being  that  described  by  a  point  a  of  Fig.  263 
in  the  meridian  circle  be  when  rolling  upon  the  base  circle  cd. 
The  center  of  curvature  is  always  upon  the  surface  of  the  sphere 
and  never  at  an  infinite  distance  and  the  involute  crown  gear 
tooth  side  has,  in  consequence,  the  curved  form  indicated.1 

The  introduction  of  the  straight-sided  crown  gear  tooth  as  in 
Fig.  262  produced,  therefore,  an  entirely  new  set  of  curves  in 

1  The  rack  is  a  limiting  case  of  the  crown  gear.  As  the  diameter  of  the  crown 
gear  increases,  the  base  sphere  also  increases.  When  the  diameter  of  the  gear 
becomes  infinite  the  gear  becomes  a  rack.  Simultaneously  the  sphere  becomes 
of  infinite  diameter  and  with  it  the  radius  of  curvature  of  the  tooth  profile. 


GEAR  CUTTING 


261 


FIG.  264. — Fellows  gear  shaper,  generating  system. 


FIG.  265. — Action  of  the  Fellows  gear     FIG.  266. — Cutter  of  the  Fellows  gear 
shaper.  shaper. 


262  METHODS  OF  MACHINE  SHOP  WORK 

the  bevel  gear  teeth.  To  this  system  of  tooth  forms  the  name 
octoid  has  been  given  by  George  B.  Grant  because  the  outline  of 
the  path  of  contact  between  two  complete  gear  tooth  forms  is  a 
curve  having  a  shape  somewhat  like  the  figure  eight  as  shown  in 
Fig.  262. 

THE   FELLOWS   GEAR  SHAPER 

The  leading  representative  of  the  generating  process  for 
spur  gears  is  the  Fellows  gear  shaper  shown  in  Figs.  264  and 
265,  the  principle  of  the  action  having  been  shown  in  Fig.  257. 
Fig.  264  shows  the  complete  machine  with  the  cutter  in  position. 
The  gear  blank  arbor  is  shown  at  the  right,  the  action  of  the 
cutter  on  the  blank  appearing  more  clearly  in  Fig.  265.  Cutter 
and  blank  revolve  slowly  as  the  cutter  reciprocates  vertically. 
The  appearance  of  the  cutter  is  shown  in  Fig.  266.  It  also  is 
generated  from  an  ideal  or  imaginary  rack  tooth  represented 
by  the  side  of  an  abrasive  grinding  wheel,  the  final  generation 
being  done  after  the  cutter  is  hardened.  The  machine  for  do- 
ing this  which,  of  course,  is  found  at  the  works  of  the  makers 
only,  is  of  the  highest  degree  of  precision. 

THE   ROBBING   PROCESS  OF  GEAR  CUTTING 

The  hobbing  process  is  a  modification  of  the  generating 
process  and  was  originally  developed  to  a  commercial  basis 
by  the  production  of  machines  for  sale  in  Germany.  The  prin- 
ciple of  this  method  of  attack  is  shown  in  Fig.  267,  in  which 
the  hob  is  represented  by  a  worm,  the  two  differing  from  one 
another  by  the  fact  that  in  the  hob  the  threads  are  gashed  to 
form  cutting  teeth  as  already  shown  in  Fig.  44.  The  dotted 
outline  indicates  the  imaginary  rack  which,  in  axial  section, 
is  represented  by  the  worm. 

The  pitch  of  a  hob  as  used  in  Fig.  43  for  cutting  worms  has 
its  pitch,  measured  parallel  with  its  axis,  equal  to  that  of  the 
worm  which  it  is  to  cut,  but  the  hob  for  cutting  spurs  has  its 
axial  pitch  so  modified  that  the  pitch  measured  on  the  normal 
to  its  helix  is  equal  to  that  of  the  gear  to  be  cut.  In  action,  the 
hob  is  adjusted  at  an  angle,  as  shown  in  the  plan  view  of  Fig.  267, 
such  that  the  tangent  to  the  helix  is  parallel  with  the  teeth 


GEAR  CUTTING 


263 


to  be  cut.  At  the  beginning  of  the  cut  the  hob  is  presented  to 
the  side  of  the  blank.  The  feed  is  double — that  is,  the  gear 
blank  revolves  and  as  it  does  so  the  hob  is  fed  slowly  across  it. 
The  cut  is  continuous,  the  gear  being  completed  as  the  hob 
leaves  its  further  edge.  The  axial  section  of  the  hob  being 


Worm  representing 
the  Hob  which  cuts 
the  Gear 


FIG.  267. — Principle  of  the  nobbing  process  of  gear  cutting. 

that  of  a  rack,  the  result  is  to  produce  conjugate  forms  in  the 
gear  just  as  the  reciprocating  tool  of  the  same  profile  produces 
conjugate  forms. 

By  suitable  adjustments,  with  means  for  which  the  machines 
are  provided,  helical  gears  may  be  cut  with  the  same  facility 


264  METHODS  OF  MACHINE  SHOP  WORK 

as  spurs.  Except  for  a  few  special  machines  which  have  not 
been  placed  on  the  market,  this  is  not  true  of  other  spur  gear- 
cutting  machines.  There  is  no  doubt  that  the  use  of  helical 
gears,  the  merits  of  which  are  unquestioned,  has  been  held  in 
check  by  the  lack  of  facilities  for  making  them,  and  the  hobbing 
machine,  by  providing  these  facilities,  has  already  had  a  decided 
influence  in  increasing  the  use  of  this  type  of  gear. 

THE  GOULD  AND  EBERHARDT  GEAR -HOBBING  MACHINE 

A  gear -hobbing  machine  by  Gould  and  Eberhardt  is  shown 
in  Figs.  268  and  269,  the  former  showing  the  machine  as  set 
up  for  cutting  spur  gears,  the  blank,  not  shown,  being  mounted 
on  the  vertical  arbor  and  the  hob  on  the  arbor  of  the  swivel 
head  on  the  column.  Fig.  269  shows,  more  in  detail,  the  adjust- 
ment and  the  action  when  cutting  helical  gears. 

THE  TEMPLET   SYSTEM  OF  GEAR  CUTTING 

For  large  cut  mill  gears  the  templet  system  is  most  commonly 
resorted  to.  For  such  gears  the  cost  of  special  cutters  becomes 
prohibitive  while  a  templet,  which  is  the  only  special  feature 
required  for  cutting  any  gear  by  the  templet  system,  costs  but 
little  and  may  be  easily  made  for  special  cases  as  they  arise — 
and  mill  gears  are  usually  special  cases.  A  representative  of 
the  templet  system  is  found  in  the  Newton  floor -plate  machine 
shown  in  Fig.  270.  Any  diameter  of  gear  may  be  accommo- 
dated by  adjusting  the  distance  between  the  cutting  tool  and 
the  center  of  the  blank,  this  machine  sharing  with  other  floor- 
plate  tools  the  feature  that  it  prescribes  no  limit  to  the  size  of  the 
work  which  it  can  accommodate.  The  indexing  mechanism  is 
under  the  floor  and  hence  out  of  sight. 

Fig.  271  gives  an  outline  plan  view  of  the  action  of  the  tem- 
plet which  is  here  divided  in  halves — one  for  each  side  of  the 
tooth  spaces.  By  suitable  feeding  mechanism,  into  the  details 
of  which  it  is  not  necessary  to  go,  the  tool  is  guided  by  the 
rollers  a  b  which  ride  on  the  templets  c  d.  In  actual  use  but  one 
of  the  templets  is  in  position  at  a  time,  thus  avoiding  their 


GEAR  CUTTING 


265 


nice 


FIG.  268. — Gear  bobbing  machine  set  for  spur  gears. 


FIG,  269. — Gear  bobbing  machine  set  for  helical  gears. 


266 


METHODS  OF  MACHINE  SHOP  WORK 


interference  with  one  another  which,  from  the  illustration,  might 
be  inferred  to  take  place. 


FIG.  270. — Floor  plate  gear  cutting  machine,  templet  system. 


FIG.  271. — Principle  of  the  templet  system  of  gear  cutting. 

The  application  of  the  templet  system  to  the  cutting  of  bevel 
gears  is  shown  in  Fig.  272  from  the  Gleason  Works.  The  arm — 
seen  endwise — which  carries  the  planing  tool  moves  about  the 


GEAR  CUTTING 


267 


cone  center  of  the  gear  to  be  cut,  and  in  its  movement  is  guided 
by  the  templet  a  on  which  a  roller  attached  to  the  arm  rides. 
The  templet  has  the  outline  of  the  desired  tooth  profile  suitably 
enlarged  to  provide  for  its  increased  distance  from  the  cone 
center. 

Contrasting   the   generating   and   the   templet   systems  as 
applied  to  bevel  gears,  the  former  is  limited  to  the  smaller  pitches 


FIG.  272. — Gleason  bevel  gear  cutting  machine,  templet  system. 

because,  in  comparison  with  their  capacity,  generating  machines 
must  be  much  heavier  than  templet  machines.  The  former 
is  essentially  a  manufacturing  while  the  latter  is  a  making 
machine. 

THE  GEAR-MOLDING   MACHINE 

Heavy  gears  are  frequently  made  with  cast  teeth.  The 
earliest  method  of  doing  this,  which  is  still  much  used,  though 
not  to  be  recommended,  was  to  mold  them  from  complete  pat- 
terns. Such  patterns  are  expensive  and,  moreover,  it  is  not 
practicable  to  make  and  space  so  many  pattern  teeth  with  a  sat- 
isfactory degree  of  accuracy.  Added  to  this,  the  patterns  being 


268 


METHODS  OF  MACHINE  SHOP  WORK 


of  wood  soon  warp  and  shrink  and  so  lose  what  approach  to 
accuracy  they  may  have  when  new.  Gears  which  are  at  once 
better  and  cheaper  than  those  molded  from  patterns  are  molded 
on  gear-molding  machines1  of  which  an  excellent  example  at  the 
works  of  the  Mesta  Machine  Company  is  shown  in  Fig.  273. 
The  machine  has  somewhat  the  appearance  of  a  boring  mill. 
The  (iron)  flask  is  placed  upon  the  table  which,  by  suitable 
indexing  mechanism,  is  turned  by  hand  from  time  to  time  to 
give  the  spaces  between  the  teeth.  The  pattern  is  for  one  tooth 


FIG.  273. — Gear  molding  machine. 

only  and  hence  may  be  made  with  all  the  accuracy  possible  in 
hand  work  and  at  small  cost.  It  is  mounted  on  a  support 
depending  from  the  cross  rail.  When  in  position  the  workman 
rams  the  sand  around  it,  then  withdraws  it  radially,  indexes  the 
table  for  the  next  tooth  and  repeats  the  process.  The  molding 
of  the  arms  and  hub  being  foreign  to  the  subjects  here  discussed 
are  omitted. 

The  method  is  equally  well  adapted  to  the  production  of  spur, 
bevel  and  helical,  including  double  helical  or  herringbone  teeth 

1  Invented  in  England  about  1860  by  Messrs.  Jackson. 


GEAR  CUTTING  269 

which  last  find  large  use  in  the  severe  work  of  rolling  mills.  The 
resulting  gears  are  entirely  satisfactory  for  many  purposes. 
They  are,  however,  apt  to  be  slightly  out  of  round  because  of 
uneven  shrinkage  of  the  arms.  This  may  be  obviated  by  casting 
the  rim  and  the  center  or  spider  separately,  when,  the  rim  being 
bored  and  the  spider  turned  to  fit,  excellent  results  are  obtained. 


CHAPTER  XIII 

GRINDING 

Early  development  of  the  grinding  machine — Rough  turning  and 
finish  grinding — Uses  of  the  grinding  machine — The  planetary  grinding 
machine — The  surface  grinding  machine. 

FUNDAMENTAL  IMPORTANCE  OF  THE  GRINDING   MACHINE 

The  grinding  machine  is  the  most  recent  fundamental 
improvement.  Until  its  appearance  turned  work  was  on  the 
same  basis  that  planed  work  was  on  prior  to  Whitworth's  inven- 
tion of  the  method  of  originating  flat  surfaces  by  scraping.  The 
work  of  the  grinding  machine  is  an  exception  to  the  otherwise 
universal  tendency  toward  deterioration  of  workmanship,  the 
grinding  machine  being  the  one  machine  tool  which  produces 
work  of  the  same  quality  as  its  own  parts.  It  is  also  an  excep- 
tion to  the  general  rule  behind  American  machine-tool  design  in 
that  the  impelling  motive  which  led  to  its  original  production 
was  improvement  of  quality  and  not  increased  output. 

Like  all  mechanical  developments  of  large  importance  it  had 
its  germs  in  the  work  of  long  ago.  Mr.  Freeland  is  known  to 
have  built  a  lathe  in  1852  of  which  the  main  spindle  was  hard- 
ened and  ground — the  bearing  surfaces  being  made  by  welding 
strips  of  tool  steel  to  a  wrought-iron  body.  The  grinding  was 
done  by  a  fixture  secured  in  the  tool  post  of  the  lathe  on  which 
the  work  was  done,  which  fixture  carried  a  grinding  wheel  driven 
from  an  overhead  drum.  Solid  emery  wheels  were  not  then 
made,  the  grinding  wheel  being  a  disc  of  iron  with  a  lead 
periphery  which  was  charged  with  emery. 

Grinding  attachments  of  this  kind  came  into  considerable  use 
after  the  appearance  of  the  solid  emery  wheel  and  as  early  as 
1864  special  grinding  machines  of  the  lathe  type  were  made  by 
the  Brown  and  Sharpe  Manufacturing  Company.  The  univer- 
sal grinding  machine  of  the  present  type  was  designed  by  Mr. 

270 


GRINDING  271 

Brown  in  1868  and  the  first  machine  was  made  in  1874.  This 
machine  was  the  prototype  of  many  others  and  was,  in  fact, 
quite  as  remarkable  a  production  as  the  universal  milling  ma- 
chine and  perhaps  even  more  so,  if  judged  by  absence  of  subse- 
quent changes  which  have  been  found  desirable. 

The  original  purpose  of  the  grinding  machine  was  the  grinding 
of  hardened  steel  shafts,  thus  permitting  their  use  where  unhard- 
ened  shafts  had  previously  been  used  because  of  the  impossibility 
of  truing  shafts  after  hardening.  It  was  not  long,  however, 
before  the  machine  was  tried  on  unhardened  work  and  found 
to  do  its  work  more  cheaply  than  the  lathe — that  is  to  say,  the 
work  could  be  semi-finished  in  the  lathe  and  finally  finished  in 
the  grinding  machine  in  less  time  than  it  could  be  done  in  the 
lathe  alone,  the  workmanship  being,  at  the  same  time,  materially 
improved. 

The  practice  of  semi-finishing  in  the  lathe,  leaving  but  a  few 
thousandths  of  an  inch  for  the  grinding  machine  to  remove, 
prevailed  for  many  years,  but  has  now  largely  disappeared 
through  the  efforts  of  the  Norton  Grinding  Company,  who  in 
1890  produced  a  grinding  machine  of  unexampled  weight  and 
power.  The  wheels  of  this  machine  were  much  larger  and  were 
mounted  on  spindles  and  driven  by  belts  of  corresponding 
dimensions,  the  idea  being  to  rough  turn  the  work  in  the  lathe 
only,  the  grinding  machine  being  given  much  more  metal  to 
remove  than  under  former  practice.  Coincident,  or  nearly  so, 
with  this  development  of  the  grinding  machine  the  new  abrasives 
carborundum  and  alundum  made  their  appearance.  These 
abrasives  are  far  superior  in  cutting  qualities  to  emery  or  cor- 
undum and,  combined  with  renewed  attention  to  the  entire  sub- 
ject of  grinding  wheel  making  and  grading  by  the  Norton 
Company,  they  did  much  to  make  the  new  practice  of  rough 
turning  feasible  and  it  has  come  into  large  use.  The  Norton 
plain  grinding  machine  is  shown  in  Fig.  274. 

GRINDING-MACHINE  ADJUSTMENTS 

Fig.  275  shows  a  Brown  and  Sharpe  universal  grinding  ma- 
chine and  Figs.  276-279  show  in  outline  a  variety  of  set  ups  for 


272 


METHODS  OF  MACHINE  SHOP  WORK 


different  classes  of  work  from  which  it  will  be  seen  that  the 
name  universal  is  well  justified. 


FIG.  274. — Plain  grinding  machine. 


FIG.  275. — Universal  grinding  machine. 

Three  methods  of  making  adjustments  for  angular  grinding 
are  provided.  Tapers  of  small  angle  are  most  frequently 
obtained  by  the  swivel  adjustment  of  the  work  table  on  the 


GRINDING 


273 


main  slide  as  shown  in  Fig.    276.     More  abrupt  tapers  are 
obtained  by  the  swivel  adjustment  of  the  grinding  wheel  stand 


FIG.  278.  FIG.  279. 

Various  set  ups  of  the  universal  grinding  machine. 

as  shown  in  Fig.   277.     If  a  piece  contains  two  tapers  these 
adjustments  are  used  in  combination  as  in  Fig.  278,  one  taper 

18 


274  METHODS  OF  MACHINE  SHOP  WORK 


FIGS.  280  and  281. — Planetary  grinding  machine. 


GRINDING 


275 


being  obtained  from  the  table  and  the  other  from  the  wheel 
stand  adjustment.  For  internal  grinding  the  usual  grinding 
wheel  is  removed  and  a  belt  pulley  is  substituted  for  it.  The 
wheel  stand  is  turned  bodily  around  through  an  angle  of  180 
degrees  and  the  internal  grinding  attachment  and  a  connecting 
belt  are  put  in  place  all  as  shown  in  Fig.  279,  the  work  being  car- 
ried in  a  chuck.  For  internal  taper  grinding  the  head  stock  is 
provided  with  a  swivel  adjustment  of  which  no  special  view  is 
shown. 

THE   PLANETARY   GRINDING  MACHINE 

In  the  grinding  machine  as  so  far  described  the  arrangement 
is  always  such  that  the  work  revolves.  There  are  many  cases, 
especially  in  internal  grinding,  in  which  the  outside  dimensions 
of  the  work  are  such  as  to  make  it  impracticable  to  revolve  it  and 


FIG.  282. — Principle  of  the  planetary  grinder. 

for  work  of  this  type  the  planetary  grinder  was  developed  by  the 
Heald  Machine  Company.  A  machine  of  this  type,  arranged 
for  the  grinding  of  the  internal  surface  of  automobile  cylinders, 
is  shown  in  Figs.  280-281. 

The  diagram,  Fig.  282,  shows  the  mounting  of  the  grinding 
wheel  spindle  a  eccentrically  within  the  bush  b  which,  in  turn,  is 
mounted  eccentrically  within  the  greatly  enlarged  main  spindle 
c.  The  bush  b  may  be  adjusted  circumferentially,  the  eccentric- 
ities being  so  proportioned  that  when  the  bush  is  turned  half 


276 


METHODS  OF  MACHINE  SHOP  WORK 


around  from  the  position  shown  the  centers  of  a  and  of  c  coin- 
cide, in  which  position  of  the  parts  if  c  be  revolved  the  position 
of  a  will  be  stationary.  By  adjusting  b  the  center  of  a  may  be 
made  to  travel  in  a  circle  of  any  diameter  desired  up  to  the  one 
shown  in  dotted  lines  as  a  maximum  and  by  this  adjustment  the 
size  of  the  work  to  be  ground  is  accommodated,  the  range  of  the 


FIG.  283. — Vertical  planetary  grinding  machine. 

adjustment  being  supplemented  and  increased  by  varying  the 
diameter  of  the  grinding  wheel.  The  appearance  of  the  rear 
end  of  the  grinding  spindle  and  of  the  eccentric  bush  with  the 
method  of  driving  the  spindle  are  shown  in  Fig.  281,  in  which 
also  the  gear  for  driving  the  large  main  spindle  is  shown. 

The  planetary  principle  has  been  applied  in  Germany  to  classes 
of  work  to  which  grinding  has  not  been  adapted  in  United  States. 
Fig.  283  shows  a  vertical  planetary  grinding  machine  by  Frie- 


GRINDING  277 

drich  Schmaltz.  The  mechanism  of  the  vertical  head  stock  by 
which  the  planetary  action  is  obtained  does  not  differ  in  principle 
from  that  already  shown  in  connection  with  the  Heald  machine. 
The  work  table  is,  however,  of  an  entirely  different  character  and 
to  it  work  of  large  size  and  of  a  great  variety  of  forms  may  be 
secured,  the  machine  being  used  for  external  as  well  as  internal 
grinding.  Thus  a  locomotive  link  with  its  eccentric  rod  pins 
in  place  may  be  strapped  to  the  work  table  and  the  pins  be 
ground  in  position  by  the  planetary  traverse  of  the  grinding 
wheel  around  them.  Likewise  the  holes  in  the  links  may  be 
similarly  ground,  neither  of  which  operations  is  possible  with 
the  usual  type  of  machine  because  the  dimensions  of  the  link 
are  such  that  the  usual  machine  will  not  swing  it. 

The  illustration  shows  the  machine  fitted  with  a  supple- 
mentary work  table  having  a  radius  arm  projecting  from  its  rear 
through  the  frame  of  the  machine.  By  locating  a  center  at  a 
point  on  this  arm  such  as  to  provide  the  desired  radius,  a  loco- 
motive link  may  be  strapped  to  the  supplementary  table  and  the 
link  arc  be  ground.  To  accomplish  this  it  is,  of  course,  neces- 
sary that  suitable  connection  be  made  between  the  main  and  the 
supplementary  tables  so  that  the  straight  line  feed  traverse  of 
the  main  table  is  transmitted  to  the  supplementary  table  in  the 
direction  of  the  arc  of  a  circle. 

It  is  clear  from  what  has  been  said  that  a  hardened  link  may 
be  bolted  to  the  table  and  its  link  arc  and  eccentric  rod  pin  holes 
be  ground  at  the  same  setting — the  planetary  action  of  the 
wheel  being  brought  into  play  when  grinding  the  holes  but 
suspended  when  grinding  the  link  arc. 

An  even  more  ambitious  German  planetary  grinder  by  the 
same  maker  is  shown  in  Fig.  284.  This  machine  is  intended  to 
grind  locomotive  crank  pins  after  they  have  been  forced  into 
place.  While  the  machine  is  somewhat  complex  in  appearance 
its  action  is  simple.  The  grinding  wheel  is  mounted  upon  a 
frame  carried  by  a  cross  arm  which  in  turn  is  carried  by  the  main 
spindle  of  the  machine.  The  action  of  the  spindle  is  to  carry  the 
wheel  in  planetary  fashion  around  the  pin.  The  driving  wheels 
with  their  shaft  are  mounted  on  offset  V's  so  located  as  to  give 
the  desired  radius  to  the  crank  arm. 


278 


METHODS  OF  MACHINE  SHOP  WORK 


FIG.  284. — Planetary  grinding  machine  for  grinding  locomotive  crank  pins. 


FIG.  285. — Surface  grinding  machine. 


GRINDING  279 

THE   SURFACE -GRIND ING  MACHINE 

An  adaptation  of  the  grinding  process  to  the  production  of 
flat  surfaces  is  shown  in  the  Pratt  and  Whitney  surface  grinder 
of  Fig.  285.  The  grinding  wheel  is  of  cup  form  and  past  it  the 
work  reciprocates  after  the  manner  of  cylindrical  grinding 
machines.  A  guard,  partly  removed  in  the  illustration,  pre- 
vents the  flying  of  the  water  with  which  the  work  is  flooded  to 
absorb  the  generated  heat. 


INDEX 


Accuracy,  absolute  is  not  obtainable, 

135 

and  interchangeability  not   synon- 
ymous, 23 

a  source  of  economy,  21,  53 
of  form  has  no  unit  or  gage,  28 

method  of  specifying,  29 
of  measurement  as  related  to  char- 
acter of  surfaces  measured,  79 
of  position,  measuring,  103 
the  three  kinds  of,  28 
Allowance,  tolerance  and  limit  denned, 

136 

illustrated,  138 
Angles,  originating  by  the  adjustable 

angle  plate  method,  50 
by  the  scraping  process,  42 
by  the  sine  bar  method,  49 
by  the  two  disc  method,  45 

B 

Bar,  the  boring,  185 

for  spherical  seats,  189 
for  taper  holes,  186 
the  pilot,  166 
Base  line  drawings,  214 
Belt  shifter  for  cone  pulleys,  147 
Bodmer,  John  G.,  the  work  of,  5,  6,  9 
Boring  and  turning,  151 
bar,  see  Bar,  the  boring, 
machines  for  vertical  cylinders,  189 
mill,  the,  153 

development  of,  156 
the  floor  plate,  195 
the  turret,  159 
tool,  revolving,  219 
Brown,  D.  R.,  the  work  of,  9,  227,  234, 

270 

Button  method  of  accurately  spacing 
holes,  217 


Caliper,  the  micrometer,  90 
the  Brown  and  Sharpe,  92 
the  Slocomb,  90 
of  James  Watt,  82 
for  measuring  screw  threads,  128 
origin  of,  90 

or  snap  gage,  origin  of,  9 
the  vernier,  80 

origin  of,  9 

Calipers  contrasted  with  gages,  1 14 
reducing  the  error  of,  80 
source  of  error  in  using,  79 
the  merits  of,  1 14 
Cam  cutting  machine,  the,  244 
Chuck,  the  collet,  163 
Cone  pulley  belt  shifter,  147 
defects  of  the  conventional,  143 
improvement  of  the,  144 
Cost  of  gages,  high,  118 

increase  of,  with  reduction  of  toler- 
ance, 141 

as  influenced  by  workmanship,  21 
of  special  tools  as  related  to  saving, 

161 

Credit  to  inventors,  giving,  i 
Cutter  grinding  machine,  the  milling, 

247 

Cutters  for  milling  machines,  232 
Cylinder  boring  machine,  vertical,  189 

D 

Darling,  Samuel,  the  work  of,  9 
Degradation    of  workmanship,    tend- 
ency toward,  23 
Depth  and  height  gages,  80 
Dial  gage,  applications  of,  104 
Diametral    pitch  system,   advantages 

of,  6,  250 
Disc    method    of    accurately    spacing 

holes,  219 
of  originating  angles,  45 


281 


282 


INDEX 


Division  of  functions,  the,  56,  90,  117, 

214 
Drilling,  199 

example  of  multiple  spindle,  209 
heads,  multiple  spindle,  205 
jigs,  292 

transfer  of  holes  to,  from  master 

plates,  222 

machine    for    accurate    spacing    of 
holes,  210 
gang,  204 

multiple  spindle,  205 
radial,  199 
station,  204 
types  of,  199 
upright,  199 

Drawings,  base  line,  214 
Driving  systems  for  machine  tools,  143 


Edges,  straight,  applications  of,  32 
End    and    line    measures,    differences 

between,  17 
measures,  accuracy  of,  78 

characteristic    of    manufacturing 

system,  14 
illustrated,  16 
Errors,    source    of    when    using    line 

measures,  79 
of     line     measures     and     calipers, 

reducing,  80 
measurement  of,  97 

with  extemporized  apparatus,  no 


Factory  organization  as  influenced  by 

measuring  system,  18 
Fits  and  limits,  135 

press,  17 

running,  17,  140 

shaft  and  hole  bases  of,  137 

taper  press,  141 
Floor  plate  boring  mill,  195 

tools,  characteristics  of,  191 

tools,  examples  of,  194 

work,  191 
Freeland,  A.  M.,  the  work  of,  29,  64, 

77,  270 
Function  of  stiffness  in  gages,  the,  in 


Functions,  the  division  of,  56,  90,  117, 
214 


Gages,  in 

of  Bodmer  and  Whitworth,  8,  16,  77 
Brown  and  Sharpe  reference  disc,  77 
characteristic  of  manufacturing  sys- 
tem, 14 
combination,  the  Johansson,  1 20 

application  of,  124 
contrasted  with  calipers,  114 
the  defects  of,  1 14 
dial,  applications  of,  104 
depth  and  height,  80 
expedients  when  using  large,  1 13 
the  function  of  stiffness  in,  in 
height  and  depth,  80 
high  cost  of,  118 
large,    stiffness   must   be    sacrificed 

to  lightness  in,  in 
limit,  115 

adjustable,  118 
the  Johansson,  1 20 
the  Newall,  119 
method  of  accurately  spacing  holes, 

124,  216 
modification  of,  to  eliminate  effect 

of  wear,  116 

snap  or  caliper,  origin  of,  9 
plug  and  ring,  8,  16,  77 
screw  thread,  126 
the  star,  132 
substitutes  for,  118 
Gear  cutting,  250 

formed  tool  system  of,  252 
generating  system  of,  254 
bobbing  process  of,  262 
templet  system  of,  264 
machine,  the  Bilgram,  256 
the  Brown  and  Sharpe,  254 
the  Fellows,  262 
the  Freeland,  64 
the  Gleason,  258,  266 
the  Gould  and  Eberhardt,  264 
the  Newton,  254,  264 
automatic,  254 
origin  of,  6,  252 

of  the  generating,  254 


INDEX 


283 


Gear  molding  machine,  the,  267 

teeth,  the  octoid  system  of  bevel,  260 
Gears,  diametral  pitch,  advantages  of, 

250 

Grinding,  270 
machine,  the,  270 
adjustments,  271 
effect  of,  on  tolerance,  139 
the  Brown  and  Sharpe,  271 
the  Heald,  275 
the  Norton,  271 
the  Pratt  and  Whitney  surface, 

279 

the  Schmaltz,  276 
the  milling  cutter,  247 
the  plain,  271 
the  planetary,  275 
the  universal,  271 

H 

Height  and  depth  gages  80 

Hob,  the,  6 1 

Hobbing  machine,  the,  60 

process  of  gear  cutting,  262 
Holders,  floating  reamer,  170 
Hole  and  shaft  bases  of  fits,  137 
Holes,   button  method  of  accurately 

spacing,  217 
disc  method  of  accurately  spacing, 

219 
gage  method  of  accurately  spacing, 

124,  216 
T-square     method     of     accurately 

spacing,  223 
transfer  of,  from  master  plate  to  jig, 

222 

laying  out  machine  for  accurately 
spacing,  210 


Inch,  origin  of  the,  75 

explanation  of  the  uniformity  of,  76 
Index-plate,  construction  and  use  of  a 

large,  53 

plates,    correct   and  incorrect   con- 
struction of,  56 

duplication    method  of    originat- 
ing, 59 


Index -plates,  step  by  step  method  of 

originating,  58 

transit  method  of  originating,  54 
Indicator,  the  tool  makers',  99 
Interchangeability  and  accuracy  not 

synonyms,  23 
Inventors,  giving  credit  to,  i 


Jig,    transfer   of   holes   to,    from    the 

master  plate,  222 
Jigs,  drilling,  292 


Lathe,   automatic   for   work   between 

centers,  180 

early,  by  Sir  Joseph  Whitworth,  5 
for  turning  spheres,  186 
the  first  screw  cutting,  151 
the  Fay,  181 
the  gun,  156 
the  Lo-swing,  184 
the  pit,  153 
turret,  automatic,  172 
magazine  feed,  175 
multiple  spindle,  178 
principle  of,  156 
the  flat,  160 
the  plain,  156 
the  vertical,  159 
tools  for,  159 
Lathes,  aligning  the  V's  of,  33 

precision,  92 
Laying     out    machine     for     accurate 

spacing  of  holes,  210 
Length,  measures  of,  65 
Lever,  multiplying,  applications  of,  97, 

99 

in  the  limit  system,  99 
Limit  gages,  115 

adjustable,  118 

the  Johansson,  120 

the  Newall,  119 
system,  the,  135 

use  of  the  multiplying  lever  in,  99 
tolerance  and  allowance  defined,  136 

illustrated,  138 


284 


INDEX 


Limits  and  fits,  135 

Line   and    end    measures,    differences 

between,  17 
relative  accuracy  of,  78 
measures,  accuracy  of,  76 
advantages  of,  79 
characteristic  of  making  system, 

14 

early  development  of,  9 
necessary  for  ultimate  standards, 

80 

reducing  the  error  of,  80 
source  of  error  when  using,  79 


M 


Machine,  see  the  machine  in  question, 
tools,  characteristics  of  American,  8 
of  English,  7 
driving  systems  for,  143 
for  the  making  system,  character- 
istics of,  4 

for  the  making  system,  origin  of,  4 
for    the    manufacturing     system 

characteristics  of,  8 
for    the    manufacturing    system, 

origin  of,  8 

Machinery,  systems  of  production  of,  3 
Magazine  feed  automatic  turret  lathe, 

175 
Making  and  manufacturing  systems, 

distinction  between,  13 
used  conjointly,  4 
system,   characteristics  of  machine 

tools  for,  4 
definition  of,  3 
importance  of  accuracy  of  form 

and  position  in,  28 
line  measures  characteristic  of,  14 
origin  of  machine  tools  for,  4 
procedure  under,  17 
Manufacturing  system,  characteristics 

of  machine  tools  for,  8 
definition  of,  3 

end  measures  characteristic  of,  14 
history  of,  10 

importance  of  accuracy  of  size  in,  28 
increased  investment  required  by,  2 1 
limitations  and  disadvantages  of,  19 


Manufacturing  system,  manner  of  the 

spread  of,  15 

origin  of  machine  tools  for,  8 
procedure  under,  17 
Master  plate,  the,  220 
Maudsley,  Henry,  the  work  of,  2,  4, 

n,  151 

Measurement,  accuracy  of  as  related 
to  character  of  surfaces  measured, 

79 
of  errors,  the,  97 

with  extemporized  apparatus,  no 
Measurements,  beginning  of  accurate, 

8 
Measures,  end,  accuracy  of,  78 

and  line,  relative  accuracy  of,  78 
characteristic,    of    manufacturing 

system,  14 
of  length,  65 
line,  accuracy  of,  76 
advantages  of,  79 
and  end,  relative  accuracy  of,  78 
characteristic  of  making  system, 

14 

early  development  of,  9 
necessary  for  ultimate  standards, 

80 

reducing  the  error  of,  80 
source  of  error  when  using,  79 
sight  and  touch,  16 
Measuring  machine,  history  of,  9,  82 
importance  of  uniform  pressure  of 

contact  in,  85 

the  Brown  and  Sharpe,  10,  85 
the  Newall,  88 

the  Pratt  and  Whitney,  10,  88 
the  Sweet,  10,  84 
the  Whitworth,  10,  82 
system,    influence    of,    on    factory 
organization,    workmanship    and 
responsibility,  18 

Meter  should  have  been  abandoned,  74 
Metric     system,     the    argument     for 

inverted,  72 
the  fallacy  of,  65 

the  manufacturer's  case  against,  69 
Micrometer  caliper  for  screw  threads, 

128 
origin  of,  90 


INDEX 


285 


Micrometer,  the  Brown  and  Sharpe,  92 
the  James  Watt,  82 
the  Slocomb,  90 
Microscope,     use     of,     in     accurate 

measurements,  81 
Mill,  boring,  see  Boring  mill. 
Milling,  224 

cutter  grinding  machine,  the,  247 
effect  of  a  flood  of  cooling  liquid,  227 
machine  cutters,  232 

fitness  of  constant  speed  pulley 

drive  for,  230 
operations,  typical,  234 
the  hobbing,  60 
the  cam  cutting,  244 
the  Lincoln,  224 
the  planer  type,  23  2 
the  profiling,  242 
the  rotary  planer,  239 
the  screw  thread,  246 
the  semi-automatic,  224 
the  universal,  227 
the  vertical  spindle,  232 
Motor  drive,  difficulties  introduced  by, 

147 

field  of  the,  149 

individual  vs  group  system,  149 
Multaumatic  machine,  the,  159 

N 

North,  Simeon,  the  work  of,  n 
O 

Organization  of  factory  as  influenced 
by  measuring  system,  18 


Pilot  bar,  the,  166 
Planer,  the  rotary,  239 
Planers,  aligning  the  Vs  of,  83 
Plate,  floor,  see  Floor  plate. 

index,  see  Index  plate. 

master,  see  Master  plate. 

surface,  see  Surface  plate. 
Precision  workmanship,  see  Workman- 
ship, precision. 
Press  fits,  17 

taper,  141 
Production  of  machinery,  systems  of,  3 


Profiling  machine,  the,  242 
Pulley,  cone,  belt  shifter  for,  147 
defects  of  conventional,  143 
improvement  of,  144 
the  constant  speed,  147 

fitness  of,   for  milling  machines, 
230 

R 

Reamer  holders,  floating,  170 
Reamers  and  reaming,  168 

influence  of,  on  basis  of  fits,   138 
Reaming  bench,  compressed  air,  171 

hand,  171 

Responsibility  as  influenced  by   mea- 
suring system,  18 

Richards,  John,  the  work  of,  10,  77 
Rogers,  Professor,  the  work  of,  88,  92 
Rotary  planer,  the,  239 


Scraping   process,  application    of,    to 
originating    angles    other    than 
right  angles,  42 
to  originating  squares,  37 
to  originating  surface  plates,  30 
introduction  of,  into  the  United 

States,  29 

the  fundamental  importance  of,  29 
the  original  publication  of, 29 
Scraped  standards,  applications  of,  32 
Screw  cutting  lathe,  the  first,  151 
Screw  cutting  lathes,  precision,  92 
machine,  see  Lathe,  turret, 
thread  micrometer  caliper,  128 

milling  machine,  246 
threads,  measuring  the  diameter    of 

128 

measuring  the  pitch  of,  129,  131 
Screws  originated  by  Henry  Maudsley, 

I51 

precision,  lathes  for  cutting,  92 
Shaft  and  hole  bases  of  fits,  137 
Shifter,  belt  for  cone  pulleys,  147 
Sight  and  touch  measures,  16 
Sine-bar,  applications  of,  49 
Snap  or  caliper  gage,  origin  of,  9 
Spacing  holes  at  exact  distances  apart, 
124,  210,  215 


286 


INDEX 


Squares,  defects  of  common,  36 
Dr.  Sweet's  improved  form  of,  36 
Ludwig  Loewe  and  Go's,  method  of 

originating,  41 
originating  by  the  scraping  process, 

35 

spirit  level,  41 
the  Ingersoll  Milling  Machine  Co.'s 

method  of  originating,  39 
Star  gage,  the,  132 
Stiffness  must  be  sacrificed  to  lightness 

in  large  gages,  1 1 1 
the  function  of,  in  gages,  in 
Straight  edges,  applications  of,  32 
Station  machine,  the,  180,  204 
Surface  plates,  originating,  30 
Sweet,  Dr.  John  E.,  the  work  of,  10 

36,  84,  149 
System,   diametral  pitch,   advantages 

of,  6,  250 
the  limit,  135 

use  of  the  multiplying  lever  in,  99 
making,  importance  of  accuracy  of 
form  and  position  in,  28 
line  measures  characteristic  of,  14 
procedure  under,  17 
manufacturing,  end  measures  char- 
acteristic of,  14 
importance  of  accuracy  of  size  in, 

28 
increased  investment  required  by, 

21 
limitations  and  disadvantages  of, 

iQ 

the  manner  of  its  spread,  15 
procedure  under,  17 
measuring,  influence  of,  on  factory 
organization,  workmanship  and 
responsibility,  18 

Systems  for  driving  machine  tools,  143 
making    and    manufacturing,    dis- 
tinction between,  13 
of  machine  production,  the,  3 


Taper  press  fits,  141 

Tapers,  method  of  originating,  47,  50 

the  various  standard,  47 
Threads,  screw,  see  Screw  threads. 


Tissues,  the  use  of,  41 

Tolerance,  allowance  and  limit  defined, 

136 

illustrated,  138 

effect  of  grinding  machine  on,  139 
increase  of  cost  with  reduction  of, 

141 

the  value  of,  in  practice,  139 
Tool,  revolving  boring,  219 
Tools,  floor   plate,  characteristics    of, 

191 

examples  of,  194 
for  the  turret  lathe,  ICQ 
machine,  see  Machine  cools, 
special,  relation  of  cost  to  saving, 

161 

Touch  and  sight  measures,  16 
T-square  method  of  accurately  spacing 

holes,  223 

Turning  and  boring,  151 
Turret  lathe,  see  Lathe,  turret. 

U 

Universal  cutter  grinding  machine,  247 
grinding  machine,  271 
milling  machine,  227 

V 

Vernier  caliper,  the,  80 
origin  cf,  9 

W 

Whitworth,  Sir  Joseph,  the    work  of 
7,  26,  29,  37,  71,  74,  82,  85 

Whitney,  Eli,  the  work  of,  n,  13 

Workmanship  as  influenced  by  measur- 
ing system,  18 
influence  of,  on  cost,  21 
precision,  definition  of,  27 

example  of  the  function  of,  33 
found  where  least  expected,  27,  55 
importance  of,  27 
the  function  of,  26 
the  original  method  of,  29 
tendency  of,  toward  degredation,  23 

Worm-wheels,  method  of  originating, 
60 

Y 

Yard,  the  standard,  76 


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